The LRH is basically a slip knot. That's my point about it being unsecured. When working around it, you could snag it and release it. Yeah, lots of wraps there, but you get my drift.
Dyneema would be a choice for a static application, but I wouldn't choose to use it as a LRH. If the LRH...
You have a climber suspended with a four wrap prusik attached to an unsecured load releasing hitch. A Dyneema sewn sling at that. The screwgate carabiner could be argued one way or the other. Why have you not backed up that arrangement?
Several meters of tail on one side of the double...