I looked at the code to see what might have triggered that series of warnings in the Freemius library we include. It looks like the option they use for the active plugins appears to be not coming through as the proper value in your case.
I put together a fix for their library here: https://github.com/Freemius/wordpress-sdk/pull/487
There’s no ETA on their fix, but I will attempt to fix it on our code (note: any plugins that call a newer version of Freemius will get used and won’t have the temporary fix)