Windows Server VM disconnected if fixed IP address, not with DHCP address

Hi!

Is this black magic?

For my company of 30 employees, I'm managing a VMware ESXi 8.0 server which is running 2 Windows Server 2022 VMs, one as Domain Controller and business application host, the other as a Remote Desktop Services server to which remote workers connect to launch our business app.

Both VMs are members of the default "VM Network" and default "vSwitch0", which is connected via a Broadcom 25G NIC and 10G DAC to our UniFi switch and UniFi Dream Machine SE network infrastructure. Both VMs were configured with static IPv4s 10.0.1.10 and 10.0.1.20 (manual configuration from Windows Server 2022, not DHCP reserved leases).

For now, the Domain controller acts as our DNS resolver, but not as our DHCP server. Our UniFi Dream Machine SE still handles DHCP, plus routing and firewalling.

Until I put this server into production, we were using an old Windows Server 2008 server that served as both a DNS resolver AND a DHCP server, with the IP address range 192.168.16.0/24.

To allow a phased migration, I created a new "network" 10.0.1.0/24 on my UniFi installation and progressively assigned this network to the different ports on the router and the switch.

This morning, only the old Windows Server 2008 server and the UniFi equipment (the router, the switch and 4 Wi-Fi access points) were left on the original and still default 192.168.16.0/24 network. This afternoon I decided to choose the new network 10.0.1.0/24 as management network for the UniFi devices.

I don't know yet if it's related, but soon after I started to receive complaints from employees that they couldn't connect to the RDS server. I noticed that it was no longer reachable. Windows Server 2022 was indicating "no network". I restored minimal service by switching to DHCP, which resulted in a different IP address: 10.0.1.191 instead of 10.0.1.20. With this configuration and this address, the server is reachable again. If I restore the manual configuration 10.0.1.20, it is no longer connected and not reachable.

What I don't understand is why the RDS VM behaves like this, but not the DC VM.

Does anyone have a genius idea of what is happening and how I can get my fixed IP address working again?

Thank you in advance! :-)