Yeah, whenever the water heater conks out we're going to do a whole house filtration and softening thing but just haven't wanted to go there yet.

I would also suggest just taking the cartridge out, cleaning it, and putting it back in. I've had this problem before and cleaning everything up and making sure all the springs are properly seated fixes it.

This is exactly what I was going to say. I also have a multi-head shower and the cartridge needs to be cleaned out every 8 months or so or one of the heads will inevitably start dripping. It's a pretty easy process that really just requires a screwdriver. And remembering to turn off the water is crucial to not launch the cartridge across your shower when you get it loose 😂