The shower pan in my rig has a couple of spots that aren't supported very good from underneath so it flexes a bit. There's an inspection opening next to the drain that I've opened and done a look-see. No water, just poor support.
2015 Greyhawk 29MV
Honda CRV toad with Blue Ox baseplate
Ready Brute Elite towbar with braking system
TST 507 Flowthru TPMS