I think that the speedo cable can’t “not turn” from pinching and then work again, the core would snap and be done
But it can pull out and then make connection again
If the square ends on one of the ends might be just inside the tiny square drive part that it’s pulling out when there is strain like the engine and tranny moving on the mounts
But pinching the cable would be a one time fail as there is no allowance for it to slip so it will twist off permanently.
I would disconnect the cable from behind the speedo
And watch it as I drive to see if the center stops spinning or not
Trace the issue
Often one of the square ends breaks off, perhaps that has happened to your cable but there is sufficient friction to make it work intermittently still.
-s
