Wreckfest should be added to the list.
With the latest patch you can't play on any servers that use the Steam version of the game at all (literally all of them) unless you downgrade the game version. Which would be fine, except that these older versions do not recognize you own DLC so if you buy it you just can't use it online while Steam users can.
What makes this confusing is that there used to be a version of the game that you could downgrade to that recognized DLC and allowed you to play online, but you can't download it anymore because they released a bunch of pointless updates that seemingly don't do anything significant other than push said version out of the options menu.
GOG support can't really do anything about it apparently and it's been 7 months, the developers clearly don't care.
Hi. I can confirm that all the DLC works in multiplayer. I seem to have been able to play with the dlc cars the last time I played.
And two of my friends confirm that you can play multiplayer with the DLC cars.