During the 1 hour test, we got at least 6 messages in the queue with recurring=1 but without a token, resulting in failmails like this:
2018-05-11T09:35:02-07:00 [INFO] Entering logging context 'queue2civicrm'.
2018-05-11T09:35:08-07:00 [ERROR] Error processing message, moving to damaged store.
WmfException@sites/all/modules/wmf_civicrm/wmf_civicrm.module:227 (INVALID_MESSAGE Recurring donation, but no subscription ID or recurring payment token found.
Source: array (
))
2018-05-11T09:36:39-07:00 [DEBUG] Queue is empty.