There have been no update that correct this issue ("unrecognized database format"). The status is unchanged from when it first surfaced more than a year and a half ago.
I feel your pain. I have lost several of my best clients due to the never ending bugs and the downtime they have caused/cost. I did manage to salvage one very important client by migrating their system to a new Web based system. Sad, they had been running
their entire business on Access for the past 7-8+ years and it wasn't until O365 that problems arose that pushed them to run away from MS. That said, although it required almost a year to accomplish, it was the best decision ever! No longer tied to any vendors,
can be hosted on any host, even internally, no issue with the number of user, can perform hot backups without issue, no longer impacted by all these Microsoft Updates, much faster, ... This is the direction I am now promoting to the rest of my clients.
Now with the latest blunder Query is Corrupt ... I have no words left. If you haven't been hit by this, turn off automatic updates immediately if you are running Access 2010 or 2013 (MSI)!!!! For the other version, be sure to ensure your systems are fully updated.
Microsoft's responses just doesn't make sense to me, and God only knows what is truly going on in Redmond as Microsoft never communicates in any truly meaningful way with its users.
Deep breaths ... that all we can do as we are all at the mercy of Microsoft (and they know it)!