Had a similar situation. Good flow/pressure everywhere in the camper EXCEPT the tub/shower hot water. This showed up after owning it a few years.
Removed the tub/shower faucets and discovered the line for the hot water, which was much longer than needed, had kinked cutting off the flow.
Simply re-routed the water line and no problem since.
2012 Fun Finder XT 276 Toy Hauler & Harley Davidson Ultra Classic with Condor wheel chock
2014 Dodge Ram 2500 AT 4X4 Crew Cab 6.4 L Hemi, 373 gears, tow package, Rambox option, Revolver X2 tonneau cover, Equal-I-zer anti-sway hitch.