Epoxy probably would not hurt your PCB unless you used a lot or did the whole thing at one time with a thick/large amount, and it shrunk while curing and cracked things. I believe “potting epoxy” is a thing and designed not to shrink while curing. Epoxy isn’t really flexible either and if it cracked from the vibrations it would also crack the PCB.
I recommend conformal coating, probably the acrylic variety for a motor sensor PCB, and probably the silicone variety for most other stuff inside an esk8, like ESCs and BMSs. Just don’t cover heatsinks with silicone or polyurethane, they can only have one single coat of acrylic.
You can put any of these three inside the motor except in/on the bearings.
Me personally, before I used that epoxy, I would prefer to “borrow” some clear nail polish from my mom/sister/gf/neice/aunt/grandma/wife and use that instead…if I could not source conformal coating