Ive been trying to find a reason why the gears are switching from H to R but when in N they stay in either H or R.
We did a full service after we bought it second hand. But yet to find the solution.
(Sometimes after many tries the gear shifts into neutral)

Mine did the same when it was fairly new its a 2014,I got pissed off with it to the point i slapped it sideways and from then on it has always worked properly.So i would say something is getting snagged and stopping the movement and the slap sorted it out.

What year is the machine?

Have you taken a look at the shift linkage?