To the devs: AccuLips turns most vowels into the ‘Ih’ selection during the ‘Align’ process using existing audio files. Every viseme I’ve created with it requires re-work to correct this issue. It’s consistently bad and needs an overhaul.
I have reported this a long time ago in FT. The only remedy at the moment is to do the lip-syncing with a project setting of 60 FPS. I hope that still works, I haven’t checked it recently.
I submitted this in 2023 and it says that it is Assigned but no fix yet. It would be helpful if you could add your findings as comment in my FT entry.
Holy schniekeys I created ticket #12707 not knowing this. I updated the ticket and referenced your previous one. Wow three years?? Uh oh…
Hopefully somebody will pay attention now… 
I tested in 8.75, Issue is still present in 24FPS/30FPS
Issue is not in 60FPS as @animagic pointed in OP,
I also added my comment in AccuLips assigns wrong vowel visemes when project framerate is at 30 FPS - Feedback Tracker