If I have lucky hit + 5% chance to restore 10% primary resource to two different items in my gear do they stack? Will I have +10% chance to restore 20% primary resource for example?
Most likely each proc happens independently. So there will be 18% chance to restore 10% resource and 1% chance to restore 20%.
PS. That was for wrong initial data, see below.
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Think your odds are off.
Four possibilities:
Both proc: 0.050.05 = 0.0025, or 0.25% for 10 mana
First procs, other does not: 0.050.95 = 0.0475, or 4.75% for 5 mana
First does not proc, second does: 0.950.05=0.0475, or 4.75% for 5 mana
Neither procs: 0.950.95=0.9025, or 90.25% for 0 mana
0.25+4.75+4.75+90.25=100, so all possibilities covered, leaving:
0.25% chance of 10 mana
9.5% chance of 5 mana
90.25% of 0 mana
But its early here and my mind might not be fully awake.
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Ebonbolt, yeah, I’ve somehow read OP not as “5% chance”, but as “10% chance”. Was sleepy myself. 
1 - (1 - 0.05)^2 = 0.0975, 9.75% chance to restore any resource.
0.05^2 = 0.0025, 0.25% chance to restore 20% resource.
2 * 0.05 * (1 - 0.05) = 0.095, 9.5% chance to restore 10% resource.
So you are right.
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If it’s coming from an aspect - like the Incendiary Aspect to restore mana on burning lucky hit chance, it should only take one of the aspects. Or at least, I know I’ve seen some gear while leveling up and not having an immediate replacement gray-out some of my Disobedience aspects - it prefers whichever aspect is “better” or “stronger”.
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Otherwise, there is a loading screen tip that says Lucky Hit chances are rolled for separately. It’s still ambiguous whether they’re rolled separately for the same type of Lucky Hit chance, but I think it’s safer to assume it rolls once for each Lucky Hit chance effect you have equipped.
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The arguable thing is that Lucky Hits in general are just ridiculously and hilarious bad.
But this depends heavily on what skill you’re using, and what it’s base Lucky Hit chance is.
Something like Ice Shards has 16% base Lucky Hit. Something else like Meteor has something like 40%. Deep Freeze has a laughable 2% base Lucky Hit. The higher this base chance on the skill, the “better” Lucky Hit (and building around it) is.
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And then there’s the formula, which looks something like this…
Skill Base LH * (1 + Additive Total LH bonus) * LH Effect Chance = Actual chance for that skill to proc that effect.
The (1 + Additive Total LH Bonus) only really has the 1 there as a global constant.
What this would look like using Fireball, having 3/3 Precision Magic, using a +25 Ancestral Wand, and having 10% Lucky Hit on Gloves, with 5% on a Ring, as well as using the 20% Lucky Hit while you have a Barrier aspect - and trying to math out ONE of those 5% Chance to restore 10% Resource…
Fireball’s Base LH chance = 33% (0.33)
Additive: Precision Magic = 15% (0.15)
Additive: +25 Wand = 15% (0.15)
Additive: Gloves = 10% (0.10)
Additive: Ring = 5% (0.05)
Additive: LHCwBarrier = 20% (0.20)
Lucky Hit Effect chance = 5% (0.05)
0.33 * (1 + 0.15 + 0.15 + 0.10 + 0.05 + 0.20) * 0.05 = 0.027225
2.72% chance for Fireball, with all that Lucky Hit, to refund Mana with this proc.
If we take out the Gloves and Ring…
0.33 * (1+0.15+0.15+0.20)*.05 = 0.02475 (2.475%)
Point of all this is just to point out that Sorc generally gets “enough” additive Lucky Hit bonus from Precision Magic, Wand, and if you use it, the LHCw/Barrier aspect that you don’t really “need” it on other slots.
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With all that out of the way, OP - your actual question.
If it ADDS the chance - then for 2 worn LH: 5% restore 10% resource effects, well, you’d add the chances together and get 10% chance to restore 10% resource. That would functionally double the chances above to restore mana from Fireball - if using the second one without LHC on gloves/rings…
0.33 * (1+.15+.15+.2)*.1 = 0.0495 (4.95%)
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If it treats each roll SEPARATELY, like it suggests it does on the loading screen tip…
Then it’d be 2 rolls of the original (2.475%, no gloves/rings) odds.
Which means a 2.475% chance for the first to proc, second to fail (10% resource)
Then also a 2.475% chance for the first to fail, second to proc (10% resource)
A 0.06% chance for both to proc. (0.02475 ^2 = 0.0006125625) (20% resource)
The remainder being 94.99% for neither to proc (no mana back).
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Overall here - the math would seem to suggest it’s BETTER if the odds DO NOT ADD, and rather if it rolls them separately. Although the difference is comparing 5.01% (for either/both to proc), vs 4.95% for the chance to be additive. This is a negligible difference.
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Disclaimer - The actual percentage/odds here are only calculated for FIREBALL and it’s 33% chance, assuming it’s to a single target. I’m not sure how LHC is calculated for the Area, nor do I know how it would be calculated for Ice Shard’s 5 hits, if Ice Shards is per-cast or per-hit, or how it would interact for Ice Shards piercing aspect/ricochets. Fireball is just “easier” to calculate because of the 1 hit/explosion as opposed to fussing over Ice Shards multiple hits.
Disclaimer 2 - As mentioned above, the base lucky hit chance on skills varies depending on the skill. If you’re asking this question about Ice Shards, the numbers are noticeably lower, but for the sake of being concise I didn’t want to use it in the example math because of Disclaimer 1, I don’t know if Ice Shards LHC is figured per-cast or per-hit.
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Yes, my and Ebonbolt numbers are based on “ideal” conditions where you have 100% Lucky Hit skill and no Lucky Hit Chance bonuses (and we don’t know real conditions that OP have).
There are skill descriptors extracted from game files that contain formulas for tooltip Lucky Hit values.
Some skills have per hit chances in descriptions, some - chance to proc at least once vs 1 target with full skill duration from all components (both direct damage and DoT). Of course, Lucky Hit itself get checked on any suitable hit (there are no “per cast” Lucky Hits internally).
Ice Shards tooltip Lucky Hit chance is per hit.
I was under the impression that for skills like Hydra and Firewall, the LHC is for the duration of the skill; ie: if Hydra has a base 53% LHC, that’s 53% LHC over the full 10 seconds to occur - not 53% for each hit the Hydras landed.
Which lines up more with what I saw vs expected when leveling and messing around with Hydra & Meteor enchant - I don’t remember any single cast of Hydra actually drop more than 1 meteor even though they were spitting enough bolts often enough that you’d figure the (napkin math, 4%) odds per bolt would do it more than they did.
Ah well. Nice to hear Ice Shards is per hit. Though that’d make actually mathing out the odds of LHC stuff on it a nightmare x.x
It’s only in the description. Real chance pre patch (IDK if it the same now) for each Hydra hit was 2.5%.
P.S. Lucky Hit system is a pretty good step forward, but inconsistent skill descriptions really hurt it. And mechanically it is still not ideal, because it’s ignores differences in various kind of procs. “Chance to heal”, “chance to restore resource”, “chance to reduce CD”, “chance to apply CC effect”, “chance to deal single target damage”, “chance to deal AoE damage” are all very different, but treated all the same. Ideally, “proc scalar” must be a function both of proc kind and procing skill.
Thank you everyone for the answers, but I checked and they actually stack and do not proc separately. Note that this applies only when you have the same lucky hit effect. I have two items that contain lucky hit for mana gain. One is 18% , the other is 18.9%
Check the pic for more details:
https://imgur.com/a/A2JYrrm
Probably, it applies only for subset of all procs that have fixed base chance (resource restore/heal).
Check the picture. In the character status screen it clearly states that it has 5% chance to restore 36.9% (18+18.9 from both items.)