If its the screen-Lock engaging itself as some sort of reaction to a route being uploaded/used. Then get another unit. My mate had this, and had to get a replacement. Which Garmin were cool about.
One bonus about making giltchy shit. Is that they have a well practiced replacement program.....
Garmin have said I might need a replacement device!
https://www.youtube.com/watch?v=xxs1zxMTaRs