>>128767
I've never had this problem, and I have a habit of pressing my thumbs into the bar on lifts.
Hell even on pullups I have my thumbs flat on the underside of the bar.
I use grip trainers all the time though, and with my thumbs as well.
Maybe you should just do what I do and just grip trainers all the time switching between your fingers and thumb?
I can't find a pic of it, but wrapping your fingers around one side of the grip trainer, and then squeezing it with your thumb.
First time I did that my thumbs were just dead and I couldn't apply any pressure with them for a day.
Now I do it all the time and I have massive grip strength.