Let me help break down what might have happened here. This is an interesting infrastructure issue that touches on several Azure networking concepts. A few potential reasons why your original setup stopped working:

Network Configuration Changes:

VNet peering settings might have been modified Network Security Group (NSG) rules could have been updated Subnet configurations might have changed Service endpoints status might have been altered

Integration Runtime Issues:

The manually selected region might have experienced capacity issues The runtime's network configurations might have become stale There could have been an IR version update that affected the networking stack

Cosmos DB Changes:

Firewall rules might have been modified Private endpoint configurations could have changed Network access settings might have been updated

The success with 'Auto Resolve' region suggests a few things:

The 'Auto Resolve' setting is more resilient because:

It can dynamically choose the optimal region based on network conditions It can failover to different regions if there are connectivity issues It might use a different networking path to reach Cosmos DB