thank you in advance
Another solution you can try looking into, is that this could be because you're having both the Qubes tools trying to set an automatic IP, in addition to your manual adjusted IP, at the same time. I.e. in Windows VM's if you need to use manual config, you need to disable the Qubes network tools service first, so it doesn't create conflict with the manual adjusted IP. Something similar probably needs to be disabled in your other VM; thoough it might help if you mention what OS this VM is?
If it's a typical Qubes template, then you can just copy the the template, and try uninstall the Qubes tools networking. But only do this in a cloned Qubes templates, don't do something like this in any important Qubes templates, because this is untested, and if it goes wrong, then you can just simply delete the cloned template, rather than have a major headache on your hand.