Not really a network guy but it won't take over unless you include eth0 and/or eth1 in that bridge, but why not just use the current bridge or pass-trough the NICs to the VMs directly?
That's OK, as long as you assign all the pool devices the existing pool will be imported, there can't be a "data on this device will be deleted" warning in front of any pool device.
That suggests the update isn't the problem.
Try disabling Spectre and Meltdown mitigations to see if you notice a difference, you can do that by adding mitigations=off to syslinux.cfg tne reboot, like so:
Upgrading to v6.10 and switching to ipvlan should fix it (Settings -> Docker Settings -> Docker custom network type -> ipvlan (advanced view must be enabled, top right)).
Fix the RAM problem, an uncorrectable error will halt the server.
Memtest doesn't detect ECC corrected errors, removed one or more DIMMs and see if the SEL errors stop.
Don't change the IP, see if the server gets one from the DHCP server, if it doesn't there's a problem there, or with how the serve is connecting to it.