macOS guest networking no longer connected (after installing container and/or Sequioa 15.7.5)

[natevw]

I am needing to use a macOS guest VM in UTM to get on a client's VPN this morning, but networking in the VM is suddenly not working. I've been using this VM for years without issue but now its "Ethernet" adapter shown in System Preferences is getting a self-assigned 169.254.x.x IP address and there's no routes to anything, neither the host nor its WAN that I need.

The UTM network mode is "Shared"; restarting the guest with it set to "Bridged" did not help.

Possibly complicating things:

• I'm still on Sequoia 15.7.5 (24G624) and the guest is actually Monterey 12.6.3
• the guest has Cisco® AnyConnect™ for VPN purposes (the whole reason for the VM…)

But these have never been issues before. I did semi-recently update to 15.7.5 which did give me trouble with another Virtualization-based project when the subnet IP range for the bridge100 network changed on it.

This might be the first time using UTM since that same host OS update as I only need this VM occasionally. It might actually be the first time using this VM since I installed Apple's container utility which is basically a Docker clone.

Any ideas what to try or how to further troubleshoot this?

One other complicating factor is that I've been perpetually low on disk space on the host, not critically low but tight enough that I'll likely have to shuffle more stuff off to try spin up another macOS guest but that will be my next step since I've been wanting to freshen up this guest anyway. Just would be more expedient in the short term if I could patch up whatever went wrong with the current guest — and I'm curious why/what could happen to suddenly cause this if it comes up in the future!

[natevw]

Update: after switching the guest to "Bridged" network mode and selecting my WiFi interface (← critical omission during first try) the WAN connectivity at least is restored. So I have a workaround to get to what I need at the moment.

Still curious as to what might have broken with this.

I did find:

• Network Mode: Bridged - No ipv4 connectivity #6311 (which seems to be the opposite of my case since bridged mode is working)
• [macOS Sequoia 15.7 + UTM 4.7.4] Shared/Bridged network and Cisco AnyConnect issues — no NAT, no extensions, VPN service unavailable #7472 (comment) (which does seem likely related?!)
• MacOs Network Configuration diagnostic tool? #7189 has a number of links/cross-references I might try return to for clues