Please see this thread from the beginning of April.
https://community.ipfire.org/t/high-memory-consumption-dns-proxy-server/15646
Yes it is a known issue. No it is not fixed in CU202 but it will be fixed in CU203 with the replacement of unbound with knot.
The simplest workaround is to disable the DNS Firewall and wait to use it when CU203 is released.