It probably is a mixture of both psychology and board.
Did you have your injury on the first board or the new one?
I am recovering from a knee injury and I have to deal with the distrust I have of my knee and the lack of surfing fitness from a 4 month lay off so I appreciate what you are going through
A suggestion is go a little longer and a littler wider so you have stable platform to pop up and make the drop.
Getting back to your old level is a challenge and you need to consider both the rehabilitation of your knee and your abilities step by step.
Choose slightly less challenging waves for a while get your act and your confidence back on them and slowly work your way back to them.
IMPORTANT;
See a sports physical therapist who can advise you on how to strengthen the entire muscle structure around the joints so the muscle add to the balance of the joint.
( dislocations occur more often when one set of muscles in the joint are stronger than others)
Often hyperlaxity is a product of that). There are other less common reasons for hyperlaxity of ligaments and they need to be clearly diagnosed by a sports doctor.
Appropriate board, physical therapy and then time enough to get your psychology backing you.
Patience.

Also about your level of surfing I still think you are over estimating your level, I read through your post and our previous conversation and I think you are trying to ride a board that is unstable because it is too small and you are having to take off more critically and do't have the full skills to do it. Trying to take too late too hard often will cause injury in the wipeout.
It adds up pretty much to that. Continuous wipeouts on takeoff also mess with your head.
Have a read of what you were advised and see if it fits!
I've taken up troll hunting just for fun, instead of a rifle I'll just use a pun! 冲浪爷爷