mt7622 unstable on 23.05, especially when using 802.1x dynamic VLANs

I have a couple of Linksys E8450s that I use as L2 bridged access points with dynamic VLAN assignment based on Radius attributes: I have configured a single WPA2-Enterprise SSID and users get assigned to a VLAN based on their attributes in the RADIUS server. I also configured roaming with 802.11r and the whole R0KH/R1HK keys.

This worked well enough until I upgraded to 23.05.2, after which I started getting really weird behaviour: some devices would connect to the network but not get assigned an IP, or have working IPv4 but not IPv6, or have both and being able to ping destinations but not get TCP traffic working.

I spent the last few days pulling hair and trying a bunch of things, including one SSIDs with WPA2-PSK per VLAN, to varying degrees of success, but things were never 100% working as intended.

As a last ditch attempt, I reverted to 22.03.5 and the dynamic VLAN config (restored from backup, so it's the exact same) and things seem to be back to how they used to be.

No file, test, or entry point is identified. Compare 23.05.2 with the restored dynamic VLAN configuration on 22.03.5, focusing on 802.1x/RADIUS assignment, 802.11r roaming, and the IPv4, IPv6, and TCP symptoms; done means identifying and confirming a fix for the regression.