Jake, we are not actually employees of UBBCentral; the team (Isaac, the beta testers, and I) comprised of private developers and volunteers who provide coding services for UBB.threads on behalf of UBBSystems (the script vendor), and provide free user to user support on the forums in our spare time.
We are web developers, and not server technicians, but we've been attempting to work through your issues by comparing data from your PHPinfo and System Requirements Test output to working configurations and we're really not sure what could be the cause of the issues on the page. The login page being displayed is actually part of an error that is being triggered to obscure the page from users, it is being triggered by a server fault of some sort, but I'm not entirely sure of the cause.
We also tried various permutations with your config file on our servers while testing to attempt to recreate the error but could not. You should be able to disable the spider friendly URLs and see if it opens the community again (changing the "SEARCH_FRIENDLY_URLS" value in your config.inc.php file to a 0), though that would leave you with no spider friendly URLs on PHP7; or, if it was working properly in PHP5, you might have your server techs roll the system back until a cause to this issue can be pinpointed. We've tested this release extensively up to PHP7.3 and had not seen this issue ever pop up.
What appears to be happening is the system is not parsing URLs with basic separators (?&;=/ characters in URLs), and I have no idea what PHP settings or variables could affect that behavior.
It may be a long shot, but did your host restart your machine after building the PHP7 kernels and after updating EasyApache? If you're not on a dedicated machine, is it possible for your host to move you to another machine (that woudn't have 17 year old settings like the MySQL password issue)?
