Not OP, but facing the same issue since updating to 7.22 and I’ve downgraded one router to 7.21.3 for some troubleshooting.
Routing table on 7.21.3 of the very same container:
$ ip rule list
90: from all masquerade
200: from all lookup local
5210: from all fwmark 0x80000/0xff0000 lookup main
5230: from all fwmark 0x80000/0xff0000 lookup default
5250: from all fwmark 0x80000/0xff0000 unreachable
5270: from all lookup 52
2147483646: from all lookup main
2147483647: from all lookup default
And on 7.22:
$ ip rule list
1: from all lookup local
2: from all lookup main
3: from all lookup default
5210: from all fwmark 0x80000/0xff0000 lookup main
5230: from all fwmark 0x80000/0xff0000 lookup default
5250: from all fwmark 0x80000/0xff0000 unreachable
5270: from all lookup 52
anything specific I can check?
It’s table 52 which is not accounted for, since the lookup to main happens with a higher priority; adding an explicit routing rule in main mitigates the issue