Tried upgrading my RB751U-2HnD,
The files uploaded ok but upon rebooting to upgrade it didn’t come back up 
Managed to reset the RB and load an old backup config from December last year, sure I had more recent backups but they might be on the other pc…
Either way something in my config seems to have choked the upgrade process but not sure what.
Sadly I think any useful logs will have been nuked in the reset 