TS, I assume your caches were loaded via PQ's?
It is still quite common for the Montana to have trouble indexing random geocaches, and when the issue occurs, the Montana simply ignores the entire GPX file. This bug is as old as the Montana itself, and Garmin has yet to cure it.
This is why I keep all my GPX and other data on the uSD card. When this occurs,, I only need to remove the uSD card, reboot the Montana to refresh/clear the memory, reinsert he uSD card and reboot again. This procedure is almost always successful.
If you do not have a back up copy of the Montana as you received it, you can enter recreational profile, connect to computer, back up your GPX and POI (etc) directories as well as your maps, delete all files/folders from the unit, remove uSD card, reboot, copy saved data back to Montana and uSD card. Original profiles with original wallpaper are available from the Montana wiki
, which need to be copied back to the Garmin\Profiles directory, and rebooted again.
Your maps and personal data will be present, but all else will be as new. I am unsure you need to do all this. Probably just keeping your data on the uSD card and knowing you will, from time to time, have to remove the uSD card and reboot the Montana empty to clear it out, then again with the uSD card installed, as outlined above.
Hopefully Garmin will address some of the Montana shortcomings
in a future firmware release.