From what I have seen there was a software upgrade. That could mean a lot of things.
I know when I was working on vBulletin-based forums, there was a whole secondary, duplicate posts database that had to be rebuilt from time to time - there is one database that users use to view content, and another whole duplicate of it that is used to perform searches on. The idea being that searches are resource-intensive and bog down the users' ability to view, edit and add data. So the forum software keeps two identical copies and then uses one for viewing/updating and the other for searching. If the two get out of synch - typically after some kind of software update, then the re-synching process takes days to chug thru and you'll often see gaps as the search copy is purged and rebuilt.
But something you have to keep in mind here...
You're giving me flashbacks.... (similar, used to mod and admin numerous forums, and do some custom code and maintain the infra as non-paid hobby).
Guys - like M@ said, it happens. Even massive sites go down in entire regions or even worldwide (Google, Etsy, ebay,
Twitter X that mess Elon is creating before it implodes), and EBR mods are fairly non-involved, let alone the much smaller set that have the skills and permissions to handle system issues or updates (may also be done for them...am completely unaware of their hosting situation).
Worst for me was jumping in during a forum outage to help in an 'emergency', to find out that particular forum (think this one was SMF, not VBB) was basically running on massively-beyond-EOL Redhat Linux (not RHEL, like 7+ versions back, massive security holes among other things) and someone had the 'wise' idea to try to update the core forum software, which of course expected/required at least a moderately recent set of dependencies, pretty much all of which were unmet. 'Surprise'?
Wound up having to unravel every single dependency, then locate a 'good enough' version to build from source, sometimes having to hack the code along the way. There also was no staging host or anything else useful so it was all 'live.' The SMF 'upgrade' that was attempted was also a huge jump, and of course - the forum backups had failed some time ago, so reverting to the old forum software wasn't a sane path either. Didn't sleep for a couple of days for the most part, but got it all back online, immediately convinced the owner to get me a temporary server (nothing was in VMs or docker), moved everything to modern-at-the-time CentOS (also supported 5-7 years vs 6 month cycle), near-latest SMF, and got backups working sanely, then swapped over. Still had numerous issues due to forum code customization that needed to be sorted, but 'better' at the end of it by far.
'Stuff happens' is the short version. I'm going to assume EBR revenue makes them enough $$ that no one wants it down, so just ride it out...and thankfully I haven't seen EBR go down many times so at least it's reasonably stable. Like m@ said, looks like a significant framework update had some hiccups - and changes like this are generally on the rarer side where things are restructured.