I have a few suggestions:
First, to play it safe, fully charge and load test your battery, and check all power connections.
You could have a failing battery that is causing the lock-up.
Next, if you have waypoints,/tracks/routes saved on your unit, something
may be corrupted. I would bring these into HumminbirdPC to
validate them, by exporting all NAV data to an SD card. Delete any dups, and look for any that have invalid or incomplete coodinates.
Once you have a good copy on your computer, I'd erase all
NAV data from your unit, then re-load the corrected set.
Next, if you are doing sonar recordings, try and do multiple
small recordings, instead of one big recording.
The unit only has so much memory, and dealing with a big
recording is going to tax it.
Next, if you are not running the newest software, first I'd
search and see if there are any problems with it. If there are not,
then I'd install it.
Good Luck.