During long ops (>1hr, e.g. large uploads/syncs): token refresh fails mid-transfer, aborts with 'token expired and refresh token is not set' or reReadToken() loops/'newToken.Valid() false'. Logs show 'successful' refresh but op fails.

Box JWT auth (no refresh token; regenerate via assertion) tokens expire in 1hr. rclone refreshes at expiry, but oauth2 lib marks invalid 10s early (clock skew). Race: reReadToken() detects invalid first (fails), renewOnExpiry() too late. Box may expire slightly early.