All of your symptoms point to a lost ground connection. I agree it is likely the ground wire to trailer frame is not connected properly, or the wire has a break somewhere. You can do a quick test by completing the ground circuit to the trailer battery negative terminal via a jumper wire, if that solves the issue then you have to search for the fault in the trailer ground wiring.
And putting dielectric grease on all the bare wire parts at connections is a good way to avoid corrosion and future problems
2020 Eagle HT 30.5 CKTS Modern Farmhouse (16" wheels, spring shackles set on lower hole of frame, SumoSprings TSS-107-40, standard kingpin, B&W Companion slider, TST-507 TPMS)
2019 F250 SRW SuperCab 4X4 SB 6.2 (10,000# GVW) 3.73 Axle 18" wheels