kernel BUG at ./include/linux/skbuff.h:4470 leads Server to Hang

Go back to standard Ubuntu kernels (currently, v5.4):

sudo apt update && sudo apt install linux-generic
sudo apt-get autoremove "linux-image-unsigned-5.5.0-*"

Or, if you really do need a later version, you can fetch a reasonably modern & supported (currently, v5.8) kernel by installing the hardware-enablement branch:

sudo apt-get install linux-generic-hwe-20.04

The kernel that caused this is likely a canonical-provided "mainline" build: a one-off binary only meant to help you diagnosing kernel problems. Do not run unsupported mainline builds in production and stop running them right after figuring out whatever bug you were tracing using them.

OVS has been broken many times and will be broken again, and the issue you ran into is likely fixed in all (distribution or upstream) supported versions.

However, do try to ask the person who caused this.

Sure its bad to have a server with an abandoned kernel that does not receive any attention for a year, but the issue that lead to the decision to do that might have also have had the potential for grave business impact and if you are unable to test after the kernel switch if you reintroduced an old bug that might end badly.