Same here! I got this exact error two days ago:
LogValkyrie: Error: FlowStep_ResolveSessionCandidates(): Candidate module [e8fa79e4-456f-5746-7b2d-9d823b56d9f0] failed validation with error: [http_error_500:valkyrie-cook-api.prod.ucs.on.epicgames.com][]
Back then, I tried starting a session twice and the issue just went away. But now it’s back, and this time I can’t start a session at all.
All my files are properly validated, there’s nothing wrong on my end. Seems like something on Epic’s side.