I do indeed use the default button for interaction as my button for Mystic Allys.
Wondering if it is a shard interaction thing.
EDIT.
Ok after doing some research not sure this a bug per se but rather wonky mechanics. Here are my findings all copied from Reddit.
There are two different sets of allies: the 2 permanent ones and the group that spawns from the inna set when you attack something. The inna group makes a subtle sound when they generate, which is key to managing wave uptime. They also appear to have a set amount of time that they exist (I haven’t timed it but I’d guess ~10 seconds). This spawn/despawn cycle is very rigid as long as you are always attacking something, nothing you can really do about it.
So for management purposes, ignore the two permanent allies and just try to use the active skill immediately after the inna group of allies spawns. Keep an ear out for the sound they make when they spawn and you can get pretty close to 100% uptime on the waves!
Never spam the active skill since you really don’t want it to go on cooldown right before a new group of inna allies spawns.
In this case its that Inna’s allies are on a hard timer, which can expire while in the wave form ending it pre-maturely. So if you press the button 0.000001s before the they are set to expire, it effectively waste the CD.
The best advise i can give, is do not spam the button. Wait at least 1s after you visually see them respawn before pressing it. Its really annoying, but it helps avoid several other bugs as well.
The best way I’ve found to use it is to go in and attack enough to spawn the max number of allies, use the Mystic Ally active ability, and don’t press it again until all of the original waves are gone and you’ve spawned new allies by attacking.
It seems like if you press the Mystic Ally active ability while you already have waves out, it doesn’t refresh those waves, but instead just eats the cooldown. If it gets out of sync again, just wait until all the waves are gone before you activate new waves.
The set-spawned allies have a time limit on their life that starts when they spawn in, 15 seconds. So if you spawn them in, run around a bit, then pop the active skill, they can run out of time right away. Ive taken to just popping the skill every time they respawn to try and limit the situations where I’m stuck with no splashy bois and a long cooldown
The way the innas set works is that attacking causes you to spawn allies, these last for x seconds. After that time, they despawn and leave places for more to spawn when you next attack.
When you press the ability, it turns the allies that are currently spawned into waves. If you press the ability 2 seconds before those allies despawn then you only get 2 seconds of waves.
The best way to deal with it is to always attack at the start of a run, spawn all the allies, then press the button to get the full duration. After that only press the button again when they have all reset and you’ve spawned a fresh batch.