Turned off the main water to install a new sink, after we turned it back on there is no hot water in one shower upstairs and very little hot water in one of the other showers. Checked the hot water heater elements and they good. Water pressure is good .
Imagine that you have some small particles of crud, calcium, whatever sitting in random places in your plumbing system slightly affixed to your pipes.
Water travels over these continuously but there is no real force or pressure on them as the water is always there on both sides.
When you turn the water off and then back on - especially turning it back on full force - these can break off and start "rolling". They will simply roll to the nearest faucet, shower, or even hot water heater.
If we are working on a house that has a showing soon my guys know to turn on the water slowly.
The repair ; -First shut off the main water again and drain the system water from a low point in the building -disassemble the hot water valve side of the shower body- remember during the entire process to be careful to not get scalded. -while someone else is opening the main water valve ever so Slightly let the debris flush out of the valve stem opening. - reassemble and SLOWLY fill the system back up to leak test it. - If this is a single handle shower body then the directions are similar but will be specific to the brand and style. - Units with anti-scald technology are notoriously prone to clogging from small debris that gets dislodged from the scenario you described.