Either I've had a massive brain freeze (entirely possible), or I've found a serious bug in 2.7. Whole blocks of cues are disappearing. It seems to be related to "Undo".
The first time it happened, I assumed it was PEBKAC, but it happened 3 or 4 more times. I know the cues were written, because I was able to restore them from previously-saved show files. I don't know if other data are erased.
Jeff, If you haven't already, export the console logs (File > Export >Logs) and send the zip file to tech service:
That will help them diagnose the problem, especially if you can provide the time that the errors occurred. Also, more information about your system would help - which console, is the console a backup or master, any unusual devices or networking setups, etc.
Had the same thing happen on a show last week.
Running the latest 2.7.0 on a new Eos Ti.
Did a two step undo, the two actions I was undoing had nothing to do with cues, recording cues, etc. After the undo, I noticed I lost about 13 cues. Like with the OP, I was able restore the missing cues from a previous save.
Unfortunately, I don't have access to the console to get logs. It did only happen once, & I didn't have any problems for the rest of the Production.