Error when launching server solved this by installing mono-complete. Which mono package do you run?
Prerequisites suggests mono-devel, but it’s possible that it’s not enough. Still, I think yours is first report.
Is this two jobs on the same system with the same destination type, and are any of them an S3 backup? System.Reactive came in with S3 MinIO, but I’m not sure which of your warning lines was the initial one.