honestly, if your line trace seems ok and your mesh seems ok, it looks like a glitch / bug / thing not cool and if i was in your situation i would now open a thread in answerhub and ask for an epic staff member opinion.
Last thing i would try before answerhub : Have you the same issue in a new project ? If yes, you may need a verify of your engine. If no then your project has a trouble and you’d better migrate.