Unable to change server IP

[zaitz]

Hi!

I am in process of phasing out an old Windows 7 server, with the main role of MySQL and a small Scada application.
The server has the ip of 192.168.10.15 and I want to replace it with a vm. Everything is ready and setup, as far the vm is up and working on ip 10.205. Now when I change the IP of the Windows 7 computer to 192.168.10.14, everything seems to be working - I can remote into it with the new IP and also ping it. Ipconfig /all shows everything as expected.
Next I want to move the VM (Ubuntu) to 10.15. Right after I do it, I lose connectivity to the VM.
Now, if I unplug the Win7 machine set to 10.14, the Ubuntu machine regains connectivity.

On another try I first disconnected the old machine first and then moved the new VM to 10.15 - Everything works as expected.

I don't understand what is causing this behavior. I cleared the ARP cache ja checked the DHCP static mappings, I even restarted PFSense. Still, these two machines wont run together.

Any tips on how to troubleshoot this?

Best regards