Remote Control Locked

This has happened a couple of times. The throttle/gear lever is totally locked and imovable. I switch off the engine and when I restart the gear and throttle lever work normally.
I need to take off the remote control when next at the boat and have a look for anything coming loose etc but any pointers or thoughts might be helpful as this is really puzzling me. As the throttle was say 50% when this happened the remote would not have been trying to move the gear so may be a throttle cable issue but the engine & cables are only 3 years old and little use because of covid.
The engine is a 25hp High thrust Yamaha, I think a T25 in the USA but a FT25 here.

I had the remote control unit apart and could see nothing amiss there or the cables and connecting rods at the engine. Still puzzled.

However on reading the Yamaha remote control installation manual there is a dire warning I do not understand. It says" if the reverse throttle opening is more than 60 degrees it may lead to an error in control operation .Set the remote so that it does not turn more than 60 degrees in reverse". When I installed the engine ,3 years ago I did not do that and the angle was more like 70 degrees. Anyway I adjusted the stop doing is just less than 60 degrees.
Interestingly on both occasions I had the throttle lock I had beef going astern with a bit more power than I would normally use.
Any ideas about the remote and more than 60 degree consequences of have I found out?