Mystery temperature range on shower

[The harrymanimus]

My furthest shower from my hot water heater very occasionally does not get much hotter than luke warm. Couple times a year for the past several years. More occasionally I do notice the temp is fairly variable from day to day, where I have to adjust the temp. Some days I have to turn hot down, some days turning it all the way up isn’t quite satisfactory. Most days are at least satisfactory.

Notes:
Does not appear to be based on the temerature outside at all.
Pressure seems to not change.
Faucets nearest the shower seem to have normal temp.
I’ve excersiced the valve in hopes of noticing that temps change.
Delta Faucet Lahara 17 Series Dual-Function Shower Handle Valve Trim Kit, Stainless T17038-SS (Valve Not Included) https://a.co/d/i00uUy5

Ideas?

Thanks

 

[Tuttles Revenge]

If its intermittent and when it happens at the shower you still have full hot at the faucets, then its likely that the cartridge is defective and should be replaced. Likely the pressure balance spool or thermostat is sticking and causing more cold than being called for.

If you call Delta, they will maybe try to diagnose the issue further, but also may offer to replace the cartridge under warranty.