Netplan: Setting DNS results in "Temporary failure in name resolution"

I have multiple VMs with static IPs configured over netplan. This works as expected, but when it comes to set the DNS it's not.

My local DNS is 192.168.2.1. If I enter it and try to ping Google/another Client via the hostname, it prints “Temporary failure in name resolution”.

But if I set it to 8.8.8.8 instead of 192.168.2.1, it can resolve Google and other external sites.

Some additional infos:

• all my VMs are in 192.168.10.0
• my main network for all non VMs is 192.168.2.0
• the networks are correctly routed
• all my Linux VMs are running Ubuntu Server 20.04 and are up-to-date (also tried older Ubuntu versions)
• over DHCP everything works as expected
• Windows VMs with static IPs and DNS are also working as expected

My Netplan config:

network:
  ethernets:
    enp7s0:
      dhcp4: false
      addresses:
        - 192.168.10.13/24
      gateway4: 192.168.10.1
      nameservers:
        addresses:
        - 192.168.2.1
        - 8.8.8.8
  version: 2

resolvectl status prints the following:

Global
       LLMNR setting: no                  
MulticastDNS setting: no                  
  DNSOverTLS setting: no                  
      DNSSEC setting: no                  
    DNSSEC supported: no                  
  Current DNS Server: 192.168.2.1         
         DNS Servers: 192.168.2.1         
          DNS Domain: lan                 
          DNSSEC NTA: 10.in-addr.arpa     
                      16.172.in-addr.arpa 
                      168.192.in-addr.arpa
                      17.172.in-addr.arpa 
                      18.172.in-addr.arpa 
                      19.172.in-addr.arpa 
                      20.172.in-addr.arpa 
                      21.172.in-addr.arpa 
                      22.172.in-addr.arpa 
                      23.172.in-addr.arpa 
                      24.172.in-addr.arpa 
                      25.172.in-addr.arpa 
                      26.172.in-addr.arpa 
                      27.172.in-addr.arpa 
                      28.172.in-addr.arpa 
                      29.172.in-addr.arpa 
                      30.172.in-addr.arpa 
                      31.172.in-addr.arpa 
                      corp                
                      d.f.ip6.arpa        
                      home                
                      internal            
                      intranet            
                      lan                 
                      local               
                      private             
                      test                

Link 2 (enp7s0)
      Current Scopes: DNS        
DefaultRoute setting: yes        
       LLMNR setting: yes        
MulticastDNS setting: no         
  DNSOverTLS setting: no         
      DNSSEC setting: no         
    DNSSEC supported: no         
         DNS Servers: 192.168.2.1
                      8.8.8.8  

This is my network:

I have already tried different solutions, like modifying `/etc/systemd/resolv.conf, without success…

In the past year I had never problems about setting the DNS. The first difficulties came up two weeks ago with a newly created VM… Since there I got it never working again.

This is my first post here, so please tell me if I need to do something better or different ^^