Bathtub faucet is not responsive
To me it sounds like the rubber washer is failing, these are on the base of the stem held in by a brass screw, they do change shape over time and they do fail especially if turned off with force, luckily most plumbing stores or home stores have kits that have the different sizes needed for home repairs for 5-10$ and they can have 20 or more pieces in the kit, there are 2 or 3 standard sized ones they look like little volcanos a disk with a solid cone and a hole down the center, most hose bibs use the same style but the larger diameter, there are also flat ones and yours may look flat because of being crushed but the 3 valve showers I have installed and serviced have all had the cone shaped washers.