Stick a hose in it and see where the water goes. A lot of these go in to underground drainage and you may never se it exit. I" not crazy about drains because they take away your chems. Having a pool to full does not hurt anything.
If you got 5-6 years out of it that was very good. Most cells don't last that long. Don't worry about what caused it just get a new one. You got your moneys worth. You would have spent twice that in chlorine.
Jandy changed the connections about 8 years ago. You probably have the old ones. The ones in the link will not work if this is the case. Send a picture and I can tell you. I might can find a part number if I can see them
You could have a bad breaker that gives power to pump. New code is to use ground fault breaker on pumps. These look like they are not tripped but can be. flip it back an forth hard.
Check valves in front of the pump. They have o-rings that can go bad Check o-ring on pump lid. Make sure skimmers a full and doors are not stuck up. Your priming problem is air getting in from somewhere in front of pump.
Add a few bags of salt. Turn the AP down to about 20%. Run the pump less to save electric. Check the chlorine levels in a week or two. The apure will stop making chlorine at 52 water temp because you hardly need any chlorine with cold water.