I made an account on here specifically to comment.
I have the same exact problem with Textra, it has been driving me absolutely crazy. However, whenever you ask about it, people think that you're talking about the custom vibration pattern that Textra previously allowed you to do, so it's nearly impossible to get help on this.
I don't want Textra to have a custom vibration pattern, I simply want it to follow my global vibration pattern as I have set within Android's notification settings.
So far the only fix I've found is to install an old version of Textra and set the custom vibration pattern within the app itself. I don't want to do this, as newer versions of the app will include security fixes and other stuff. Using an old version shouldn't be an acceptable solution to this problem.
@priceless819 PLEASE let me know if you find a fix for this. I'm really frustrated with this issue and have been looking for a solution for months.
btw, I have a Galaxy S20+