Could you possibly describe in more detail what you mean exactly?
I have a relatively large ammount of users in my blog but when trying to choose an author for the article the list seems limited to 50 now when that didn’t use to be a problem.
I think this is a known issue already with wordpress core developers. There is the following ticket: https://core.trac.ww.wp.xz.cn/ticket/55749
In a nutshell: the list of users is limited to 50 for performance reasons. And as far as I can see there is no way around that.
You could try to work around this via Quick-Edit in the list of pages / posts. Unfortunately I can’t think of anything else at the moment.
