You assigned a static IP address in OS?
That's not a good idea ;-)
Inside the OS the IP address configuration must be dynamic!
If you want the private IP address of a VM to be static this is the way to do it:
https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-static-private-ip-arm-pportal#retrieve-private-ip-address-information-for-a-vm
Hope this helps.
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Regards
Andreas Baumgarten