After updating the rundeck plugin from v3.6.7 to v3.6.9 we started getting the following errors on all jobs triggering rundeck:

Instance 'main' with rundeck user 'jenkins': Notifying Rundeck...
Looking for jobId : Project:cicd/product
Could not find a job with the identifier : Project:cicd/product

Changing the API versions to match the server version (v23) did not help, but we did see a Bad Request as error message if the API version is omitted.
It seems we are also affected by this bug, though: JENKINS-22479.

A downgrade to v3.6.7 is the workaround for us, but it blocks us on fixing the tables-to-divs regression JENKINS-64142/