Why doesn't iCloud sync work when using dnsmasq, and does it work when I specify 8.8.8.8 as the server?

Question

Apple iCloud

On my home Mac mini, folders with files did not sync with iCloud, Notes partially synced and got stuck, and contacts and calendar were completely normal. Router on OpenWrt with dnsmasq. I dug everywhere until I got to the idea on the computer to manually set DNS. As put 8.8.8.8, everything started to work. The funny thing is that the router has the same DNS server, the only thing that distinguishes them is that the router caches requests. I looked at the DNS request log on the router - nothing unusual, all requests go through, even when synchronization with iCloud hangs. But, apparently, it does not answer exactly what the synchronization client expects.
Before that, I noticed another glitch: some downloads from Github with amazonaws did not work. treated in the same way. There is a suspicion that the problem is in the caching of the router. Has anyone experienced this and how to treat it? I still want to use dnsmasq so that DNS on internal addresses also works.