Maybe severely was the wrong word to use. I use RPi's in my home lab so any impact no matter how significant is limited in real world impact. In this case it was limited to loss of access to several services in my home lab for a few hours due to a complete loss of network connectivity to the server and a few hours of my time troubleshooting the issue.
The major issue was caused by moving some of the kernel modules to linux-modules-extra package. It caused an issue when I upgraded because the 8021q module needed for vlan support was moved to this package. I lost network connectivity to the first Pi I upgraded due to this. The Pi in question had an ip address assigned to the interface and to vlans configured for the interface. When networkd could not create the vlans on the interface it failed without assigning the ip address to the interface itself. I filed a ticket regarding this.
I consider the ability to use vlans to be a fairly basic expectation of a server os especially when it previously worked out of the box. I would also think vlan support to be an expected feature for the IoT gateway role pushed as appropriate for Ubuntu Core. Luckily I was able to connect to the serial console, troubleshoot and eventually correct the issue. When the module which supports a commonly used part of the ethernet family of protocols is moved to an optional package, I would expect testing of the impact to connectivity to existing deployments to take place. This led me to lose some faith in the testing done of Ubuntu on the RPi and the stability of the platform going forward. Switching platforms was easy to do in my case and so I did.
Hopefully the recommendations I made in my ticket of either moving the module back to linux-modules or adding an explicit warning to the release notes happens. The current warning regarding some modules having been moved to linux-modules-extra, without any detailing of them including the functionality they tie back to, is completely inadequate.