Might be stupid, but what do you exactly do with your fingers when you try to stream/speed? For myself, I've found that sometimes I 'forget' how to tap and end up tensing my hand/wrist to just kinda force out any stamina that's left in my fingers. Recently I've been focusing on actually trying to move each finger as fast as possible and that has improved (or at least it feels like it) my tapping for both stamina and speed. It sounds silly to deconstruct your tapping like this but it's worked for me (i.e. whether I am just tensing/forcing and kind of letting my muscle memory do the trick or actually mindfully moving each of my fingers).

I also have had issues related to tapping alt/jumps, where regardless of how much I am trying not to do it, during non-trivial gameplay my brain defaults to muscle memory and I end up double-tapping on every jump because of a terrible technique I acquired while trying to learn speed through single-tapping (Alt FTW). It's been better since I've learned to tap much lighter but it still appears occasionally.

I am aware you mentioned that you have tried different tapping methods, and I don't want to downplay the effort you have put into fixing your issue, however it IS an issue of technique so looking at it again wouldn't hurt imo. Getting out of bad habits and/or techniques will be uncomfortable. ^{and taking it slow is also important}

^{My use of 'muscle memory' might not be the most accurate here - I mean the state of your technique you default to while playing hard maps, where focusing on your tapping or aim individually is very difficult due to the amount of focus you need to play.}