It may be an issue with a security fix that came recently. You can try to extend some timeouts at the entrypoint (static configuration):
entryPoints:
# [...]
web-secure:
http:
transport:
respondingTimeouts:
readTimeout: 300s
idleTimeout: 300s
# [...]
see Traefik EntryPoints Documentation - Traefik
and Problems after Traefik update from 2.11.0 to 2.11.1: Solution inside