An attack on the Tor network should show a different warning message in Tor’s log.
Someone else reported the issue in a comment on the Tor blog:
New Release: Tor Browser 10.5a15 | The Tor Project
4/27/21, 15:57:42.781 [WARN] Not attempting connection to [scrubbed]:8443 because the network would reject it. Are you trying to send Tor traffic over Tor? This traffic can be harmful to the Tor network. If you really need it, try using a bridge as a workaround.
My cli tor is not have vpn to internet!! first hop is torBrowser.
Therefore possible an issue with Tor and unspecific to Whonix.
I am pretty sure a comment in Tor blog or post in Whonix forums will not get this fixed. A proper bug report at Tor Project’s issue tracker is required.
Please consider Generic Bug Reproduction. Specifically, Tor Generic Bug Reproduction required. Otherwise this has a very low chance of getting fixed.