Denny Cherry warns you about Big Data Clusters and keeping a particular IP address:
No problem, we just added in the correct IP range to the possible addresses for the vNet, added a new Subnet and moved the VMs over to the new subnet (which caused the VMs to reboot, but that was expected).
It turns on that BDC in SQL Server 2019 doesn’t like having the IPs changed for the aks nodes. The problem stems from the fact that BDC is generating its certificates off of the IP address of the node, so if the IP address of the node changes (even if you are using DHCP for on-prem nodes and DHCP gives you a new IP address) your BDC won’t respond.
Read on for your three possible solutions.