DNS resolving of Synology domain is sometimes not working

I have several Synology NAS:es placed on different places and I am using Synology domain *.familyds.net registerad for all of them. I use these domain names for backup between NAS:es and to connect for administration.
Sometimes (not always - most backups works) I get an error message that the backup has fail caused by DNS issues.
Sometimes when I try to connect via webinterface to administer these I get the same DNS problem.
When I have these problems I use nslookup on my Linux computer to find out if the problem:
> NAS1.familyds.net
;; communications error to 1.0.0.1#53: timed out
Server: 1.0.0.1
Address: 1.0.0.1#53

**** server can’t find NAS1.familyds.net: SERVFAIL**
> server 9.9.9.9
Default server: 9.9.9.9
Address: 9.9.9.9#53
> NAS1.familyds.net
;; communications error to 9.9.9.9#53: timed out
Server: 9.9.9.9
Address: 9.9.9.9#53

Non-authoritative answer:
Name: NAS1.familyds.net
Address: XX.YYY.ZZZ.MMM
> server 1.1.1.1
Default server: 1.1.1.1
Address: 1.1.1.1#53
> NAS1.familyds.net
;; communications error to 1.1.1.1#53: timed out
Server: 1.1.1.1
Address: 1.1.1.1#53

**** server can’t find NAS1.familyds.net: SERVFAIL**

It works when I use 8.8.8.8 or 9.9.9.9 as servers in nslookup.
I have at home Pi-Hole using Cloudflare (with cloudflared).

This problem is temporarily - When I started to write this, 1.1.1.1 could not resolve *.familyds.net but at this point of writing it can resolve the name correctly.

Do anyone have any suggestions of how to solve this problem?

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