Recently I migrated OpenVPN servers from legacy to instances; I changed UDP server from TUN to DCO. It's been working but all of sudden client (Viscosity - OpenVPN 2.6) stopped being able to download anything and in server log was:
Data Channel Offload doesn't support DATA_V1 packets. Upgrade your server to 2.4.5 or newer.
A bit strange (OpenVPN 2.6 - client and server), especially that Wireguard also stopped working (but handshakes were exchanged). It seems like setting DCO affects UDP connectivity also in Wireguard.
And once I set OpenVPN interface back to TUN, both Viscosity UDP client and Wireguard started working again.
So, that's experimental feature :-)?