the Search function for installing plugins from the WordPress repository using mainWP (admin-side) does not work when gp-premium is activated. Took me a while to figure that out as I never imagined GP would give me an issue :0)
The specific issue is exactly what I described.. the WP repository Search function just does not work.. it is a very straight-forward search: you enter some text in the Search Plugins box (upper right in this image).. then click Enter and then the repository gets contacted and filters your query.. BUT when GP premium is activated nothing happens. I cannot be much clearer than that.
Same issue even with all you modules turned off. I have a subscription with MainWP, not the free version. I have a whole bunch of their plugins turned on but have no interest in troubleshooting them all versus yours, too time-consuming when I can just turn gp-premium off.. It’s a site I use for maintenance only so I could do without GP on it if need be. But I’m sure if your understand what’s up it’ll give you hints for other little potential conflicts in other situations.