TL;DR - I hope your rollback goes well.
I also did testing for the rollback. Tests show I will need to full uninstall 7.9.12 and install 7.9.11 and then restore from a gateway backup from 7.9.9. The 7.9.12 is when Gateway OPC Connection - Type went from ‘OPC-UA’ to ‘OpcUaNextServerType’. Once 7.9.11 is installed, attempting import of a 7.9.12 project will have a parsing error, that could be common knowledge to everyone.
This rollback testing is still not successful. The last test I performed was to see if I had to redo all client side short cuts after a rollback. The answer was YES I do have to redo all client side shortcuts but I got into a situation where server side and client side were all rolled back to version 7.9.11 with clean install and redownloaded client projects. The Clients were up, scan classes were now partially synced, by that I mean that a 250ms scan, a 1 second scan, and a 10 second scan, were following a 250ms, 1sec, and 5 sec scan rate. Odd yes, but I could not get that 10 second, whether I changed it to 20 or 30 to do anything but 5 seconds. Regardless, the Active Designer changes I tried to make before or after a reboot would not push out to clients. The clients still showed live but old designs. They splash the updating project, updating cache popups, but come back as an older design that shows live values changing at 250ms, 1sec, and 5 sec.
I am still testing. * A full clean out of C:\Program Files\Inductive Automation\Ignition\data\jar-cache did not fix.
Maybe I’ll see if I can get all the the way back to 7.9.9, or go to 8.0.5 now.