Appian engine in FATAL status

Hello,
Recently we faced an issue on the production server of one of our customers, in terms that while running Appian, multiple users where seeing weird error messages.
This led us to the idea that maybe one of the Appian engines was down which was true: Process Exec 01 >>>> Status: FATAL! No gateway is active.
As a solution, we tried getting an elder version (latest working version) of the .KDB file for Process Execution 01 and duplicate it, renaming the copy with +1 name. This did not work for a couple of the elder versions as the Process engine was still in a FATAL status.
Then, we tried to repair the .KDB file that was active while we first noticed that the engine is down and this worked.
Now we have three questions:
1. What could case in the first place such event and on which log file we could see the error? – We really want to avoid this event happening again, especially since we are talk...

OriginalPostID-271926