What might be the issue with GP Premium modules not activating. I can go into the screen and activate them, they then show as active but if I refresh the screen they are not active again. I tried disabling all plugins except GP Premium with the same results.
In Tools > Site Health, can you check if there are any errors?
Also check in the server section of the info page in site health if your PHP memory limit is set to a sufficient value. Usual values are at least 128 or 256M.