I updated my m370 to 12.9 to test, I had to go back because I can't connect to the internet anymore, I read in the changelog that the routing engine has changed, could this be it?
I have been involved with the 12.9 Beta, and I have not had this issue, nor do I recall anyone posting on the beta about such an issue.
The dynamic routing engine should only potentially cause issues with more advanced routing configs. If you're not using dynamic routing at all, this likely isn't it.
If you were able to get a support file prior to downgrading, I'd suggest opening a support case and uploading that to it -- our team can take a look through it and try and piece together what happened.
WatchGuard Customer Support
we don't use dynamic routing, but I can confirm that even when I tested the 12.9 beta I had the same problem, I can no longer resolve the DNS, by the way I saw that yesterday the update was available on the site but now it seems to have disappeared, for from the webui of my m370 it keeps proposing it.
Are you using DNS Forwarding ? There is a change there.
DNS Forwarding Policy
In Fireware v12.9 or higher, when you enable DNS Forwarding, a policy named Allow DNS-Forwarding appears in the policy list. You can apply this policy to DNS traffic when DNS forwarding is enabled. For example, you might want to exclude IoT devices from DNS forwarding.
in fact, i also use dnswatch, i check, thanks Bruce