The single player mode works without any bugs or glitches so far. I bought the game on may 8th 2020.
Unfortunately the coop mode is not working at all for me. Here is my discription and I also made a video and uploaded it on WeTransfer (valid 7 days from 10.05.2020)
Here is the Link:

I retain a vehicle for coop. Then I go back to the main menu and click on "start coop". When I search for a random game or try to connect to a game hosted by my friend my screen enters the "searching for game screen" with the white wheel and the information that all progress is saved in the hosts game. So far, so good.
After that the whole interface disappears and only the starting picture with the snowy landscape and the orange Chevrolet Pickup is shown. After 30 seconds or so I'm back in them main menu like nothing happend at all. In 1 of 20-30 tries I can randomly connect to a random game when I click on "find game", but only once!

When I host a coop game the same thing as described above happens to my friend when she tries to join me. There is one difference when she tries to join me. She gets the normals screen like when you leave the coop after hours of playing with all the stats shown. (Exept that all the stats say 0 deliveries or 0% oder 0 minutes played.)
For my friend when using the "find game" feature the coop mode always works.

I opened the TCP and UDP ports in my windows firewall like describend on the website. I also opened them in my router. Nothing works. I tried to install the game on a different PC in order to test it, but I could not test it because all my progress in the cloud was overwritten with the new game status of the other PC. (Pls fix this, too!!! If you install the game on another PC and you use Cloud Save your Cloud save will be overwritten by the vanilla 0% state of the new PC you installed the game on, which is not how Cloud Save should work I think?! I already wrote a support message to Epic games about the cloud savings.)

I use windows 10 (latest windows update), a GTX 2080 (latest driver), an Intel Core I7-9700k CPU.
I use an optical fibre internet connection.

I really hope there is a solution for my problem.
I spend like 15 hours trying to get the coop working and lost my 6 hours game progress here... It was really really frustrating and disappointing and it did cost me a lot of "will power" to write this bug report as friendly as it is written now. To be honest the full version of the game is more like a inofficial closed beta at the moment, for which you have to pay at least 40€ in order to play it. Considering all the bugs in single player mode and coop mode, I find it quite outraging that most of these problems could have been avoided by an open beta in my opinion.

I'm looking forward to your reply and solutions for my problem.
Kind Regards,
A player eager to play this game without bugs eventually