You could check the db.log file as well. It might have something to do with that. As for the permission part, I believe that when you use sudo, since you run as root, bitcoin-qt probably uses root home directory and it looks for the data directory there, which is probably "/root/.bitcoin". You can check if that folder was created and if it was, there is your answer to why it syncs again.
PS: In future, don't run any programs as root unless it was intended as so by the program creators. I know it was maybe your last resort, but last thing you want is a buggy network program to be running as root on your device.
Can you post the debug.log from the start of the last session? Either the entire log or go down to the ottom o the file in a text editor and search for "Shutdown", selecting "up" instead of "down".
If nothing shows up, then use the command -debug as well to check if there's anything extra that might be missed by the regular command, that'll be a bit longer though.
Can you also state the version you're using?
If you for some reason don't want to post the reindex command, you could try the -reindex command (or it's already reindexing for you as it appears that is what you mean buy it trying to sync again.
He said the version in the OP, you missed it. "Running bitcoin client v0.14.2.0-91be5e3e-dirty on raspbian"