So I loaded a route to my Instinct (no editing, a route created with the same watch..) and that opened the gates of hell.. At first the route didn't load at all while I was at the field. When I returned I turned off the watch as I prefer to wear another watch as my daily driver in order to maximise the instinct's longevity. Anyway when I turned it back on it refused to go past the garmin logo and it also beeped at every button press. I had to apply the alternate factory reset method using the keys to bring it back to life. Hopefully my last backup was in August so not everything was lost.
I recreated the same issue by just trying to load the same route and it "bricked" the watch every time. As I really wanted to have the route loaded to my watch, I tried many times with various solutions. What did the trick was to process the route with wtracks It also helped me reduce the points of another route that had too many points and failed to load (compress option with 1 meter point accuracy). It really helped with both.