Plumbing – Pressure balance Am Stand hot and cold inlets are switched side to side. No cold water, only HOT. Remedy

I would first check the valve's anti-scalding setting. You have to take off trim and this is usually a setting on the valve outer stem. Make sure this is set to as hot as possible. This could have slipped. Next I would check the filters inside your valve cartridge. There is usually a filter for cold and another for hot. The hot filter could be clogged and need cleaning (very seldom do these need replacing except the rings).

Lastly you might need a new cartridge or to have yours rebuilt. If you know the model this might actually be easier than all of the other troubleshooting but often isn't needed. The cartridges can cost as little as $10 and up to a couple hundred.

Very odd, but here's a thought on how to troubleshoot. Shut off water pressure into your water heater. Test each one of your hot water taps. If any of them work, something is mixing cold water into your hot water pipes. Some one-handle faucet and shower fixtures can do this if their internal seals are worn out. Find it and fix it. If they all only work when water pressure is supplied to your water heater, then the problem is likely the water heater itself.

Are the other units on the same piping? If so, the mix may be caused by a recent change in their plumbing. Maybe you can engage them in the troubleshooting.