Can you attach the heightfield file: hf_barrier.png
You cannot name the tendon in the default section. Instead you should name it when you define it in the model later.
This was actually changed in 2.0. Targeting cameras now remain horizontal... have you tried 2.0?
you can also play with solimp. increasing the first two values makes constraints stronger. smaller time steps can also help.
The contact model has many parameters that can be adjusted. In your case, it sounds like you need more damping. This can be done by...
Separate names with a comma.