When you resize a PluginGui, then close out of it, and then re-open it, the minimum content size is locked to the last-opened max size of the PluginGui. Gui content ends up just getting clipped instead of scaling proportionately to the size of the PluginGui. This happens whether docked or floating.
Please see video example:
Note: As you can see from the video, only resizing it larger than the last time it was closed and then closing it again will have this effect.