Shower valve washer on hot needs replacing constantly
That washer presses up against another surface called the "seat" inside of your valve. If that seat becomes damaged or there is a buildup of corrosion on the mating surface, it tears up the rubber very quickly whenever you close the valve. Some valves have a replaceable seat. You need a special tool to remove that seat, but they are relatively inexpensive. See the picture below.


The thing is, some people wont buy that tool no matter how cheap it is and attempt to remove the seat by jamming in a screwdriver or something. That seat is soft brass, so if the screwdriver can't do the job and slips in the hole, it creates even rougher edges. They give up and resign themselves to replacing the washers much more often. Remove the stem again and take a look inside at the seat. Replace it using the tool if it looks at all rough, which I suspect will be the case.