Never had that happen before, that is strange especially since you can split and adjust the size of the sidebars out and in but not up and down. I will be looking in on this to see if anyone else posts a solution as I am curious now too as to why it is doing that. If not just for you but for me as well if mine ever starts doing this to me in the future. Sorry I couldn’t help much more
I however did come across a thread on blender stack exchange that another user was having similar problems and this was suggested to them and it fixed the problem
you can choose File > Load Factory Settings without permanently altering your existing settings (as long as you don’t save your preferences after loading). Then open your .blend and see if the problem has been resolved. The first step is to diagnose whether the behavior is caused by an add-on.