The Logic 10.5 update changed the default position of the Plugin window when it opened the first time. Instead of positioned towards the left upper corner it is now placed more in the center. If your Plugin opens in the off-center, then there is something, off.
Question, does it happen with all Plugins, how about Logic Plugins vs. third-party Plugins? Does it happen only when you open it the first time? When you reposition a Plugin, it should remember its position the next time you open it.
Maybe play with other parameters, screen resolution, discard preferences, etc.
Hope that helps,
Edgar Rothermich
Graphically Enhanced Manuals (GEM)
www.LogicProGEM.com
https://www.youtube.com/c/MusicTechExplained/