Hello, This is why you stop the the "Synchonize" before the F5 DNS upgrade. Just upgrade your devices and then again enable the dns sync. Also if you have LTM devices better to upgrade them first as written:
https://support.f5.com/csp/article/K1584488
For more information refer to:
https://community.f5.com/t5/technical-forum/knowledge-sharing-f5-software-upgrade-rma-process/m-p/291676
Also you may after the DNS HA upgrade to upgrade the big3d of any other DNS systems (if you have more than the two DNS devices that are active/standby) that are still the older version in the same DNS sync group:
https://support.f5.com/csp/article/K13734