I think it is imbalance
On a fist image, telescope is "falling", while on the second one, drive is working against the load.
The balance of the mount should
always be ideally right or adjusted such that motors are working against the load just a little. They should never be "helped" by imbalance.
Or there is a dent in worm wheel teeth in that particular place
...
Another option may be something is loose.. and it demonstrates itself when telescope is in that particulat position (imbalance issue again).
Dismantle and have a look...