Greetings,

I originally made a post about this on the update thread for Vegas 21 Build 187, this is exactly when it first started happening and the bug has now continued to build 208. Enable Automatic FX Window Resizing is unchecked.

I've made a simple video showcasing it so that hopefully Devs can fix this, as it is an extremely annoying bug for people that constantly work with VST Audio FXs since it does not only happen on window creation/opening but it also resets the FX window size every time you undo an action. Thanks!