It has always been a issue where sometimes Nemesis doesn’t pop a boss when touching a pylon.
This season, 36, I have noticed that it is more common…I just ran a rift and had two in a row fail…it has happened quite a few times and seems to be failing at a higher rate…at least for me anyways. Anybody else seeing failure that seem more than normal?
It never was an issue. When a Pylon doesn’t spawn an Elite group with Nemesis Bracer on the Follower, that only means your Follower is down the moment you activate that Pylon. Which also means, you didn’t equip them with Legendary token, relic or focus that grant them invulnerability.
When their health hits zero, you won’t benefit from any emanating powers from them. For Followers to provide for the player, you have to care about them at the first place. Get them more damage mitigation, or toss them an invulnerability token so the problem would be solved.
Read about their mechanics here.
https://maxroll.gg/d3/resources/follower-mechanics
Looking at the Enchantress focus equipped: Hand of the Prophet: gain access to all skills…
Your follower is getting Serial-Killed…
This is most likely because your follower is dead when you activate a pylon. And when a follower is dead, a legendary affix doesn’t emanate from their items to hero.
That was it,I failed to realize that I did not have Follower can not die equipped.
I am old…what can I say lol
when I started playing d3 last year it took me a while to realize this as well, so don’t feel bad. 
There’s actually one other situation where this will appear to happen: when you get an “insta kill” roll on certain enemies. My follower has the token where she can’t die and I’ve had several instances of pylons/shrines appearing to have no spawn, but with the sound of enemies dying. Usually with the “insta kill” spawn you at least see the monsters, but this season does seem to be different. It’s possible that some of the soul shards are interacting in an unintended manner here. With my Essense of Anguish unequipped I can’t replicate the lack of visual spawn (but can, as in previous seasons, replicate the insta kill spawns), but with the soul shard in my weapon I’ve had a good number of these appear to not spawn anything, right down to no loot, but can still hear the sound of the monsters dying.
I suspect the only mob type this can’t happen to are grotesques, which have a delayed death animation. I suppose I should be grateful for that since invisible insta kill spawns of those would inexplicably instagib me.
In most cases it is the follower being dead. Not always though. I’m sure bugs are bound to crop up now that the seasons are mixed with the altar, which wasn’t present for the initial incarnation of the soul shards season or any non-repeated season theme up to season 27.
In one case, for me, nemesis never spawn elite from pylon.
When I proc cheat death, and take pylon after that, lot of times elite don’t spawn.
And, that happen in both solo games (and my follower ALWAYS wear “cannot die” relic) and in group - while I play support zDH…
Maybe bug, maybe work as intended - because that 2 seconds I am not dead or alive while Awareness is active.