On one shower, the hot water flow suddenly shuts off with a thud after the shower has been running normally for a short time.

Check the mixing valve. Could be clogged. The mixing valve is what allows water to enter either the faucet or shower.

If it is the older style 2 handle with hot and cold, check the washer on the hot stem. Sometimes they get loose and will block the flow-happened to my daughter. Pulled the stem, replaced and tightened the washer, no more problems.

How often do you flush your heater? Is sounds like minerals from the water heater get into your system and clogged the inlet ports of the cartridge. Shut the water off to the valve and open it up. Remove the cartridge and check a clean the inlet ports. Before you reassemble turn the water back on to flush out the supplies. Reassemble and test. Is it better now? Let me know, Tom