Hello Viktor,
the "SID wrong len" error message above is due to a remote application that does not send a session cookie correctly. The ICM is throwing this error when trying to match the received cookie to previous active sessions and fails.
It then retries the request to the backend server that gets successfully processed. Depending on your application this may or may not be harmful.
To resolve it, SAP support, recommended to identify the remote application and resolve the issue there.
Best regards,
Menelaos