2nd floor apartment in Sacramento California not often but I have had hot water flowing out the cold side of bathroom sink, main problem is if I shut the hot water off for a short period then turn it back on for either sink or shower the water is already cold when it shouldn't be. There is something not right and I am guessing sticking check valves in the anti sweat valve.

It certainly could be the anti.-sweat valve, but it could also be the any single lever faucet in that bathroom (or another bathroom if you have one that is backed up to this one).

I would try isolating the sink in the bathroom, first. Here, if the sink faucet is a single lever faucet, shut off the hot water shutoff under the sink and then test water temperature out the faucet and see if there is an improvement. If so, then the issue could be the balancing spool of the sink faucet cartridge. If you have shut offs for the shower, you can do this test with that valve as well.

Otherwise, you may need to simply swap out the anti.--sweat valve if nothing becomes obvious after testing the sink faucet. If replacing the anti.-sweat valve fails to resolve the issue AND the shower was NOT isolatable, then that pretty much leaves the shower cartridge/balancing spool as the culprit and you'll need to replace that part, OK?

Back to you...

Mark