After some research I came in conclusion that Slipstream changes the way controller inputs are mapped after launching the game.

Steps to reproduce:
1. Connect DS4 (I connected DS4 wirelessly)
2. Launch Slipstream (and assure yourself that controller doesn't work)
3. Close the game.
4. Launch some other game ( for example, I tried playing Transistor after this and controller section in console shows "will use generic MonoGameJoystick support" instead of "will use SDL_GameController support")
5. If you want controller old behavior, remove DS4 from bluetoothctl list and pair it again.

I am not sure if I am right though. Is there going to be any fixes for this?

I know people go to GOG for a DRM-free version but if you have steam maybe try launching it as another application through bigscreen mode and have it emulate a XBOX controller. When I get the GOG version I'll look into it further.

The DS4 is a bit hit and miss when it comes to native support out of the box. From experience the DS4 will just work maybe 3 of 10 times with games bought from GoG. My wish is that developers would be a bit more zealous when it comes to implementing support for the DS4. Still haven’t tried a controller I like better.

I’m not sure what distro you are running, but I’m going to point you in the direction of ‘ds4drv’, which will let you emulate xpad controllers. This works. I played Slipstream yesterday with a DS4. If you are lucky your distro might even have ds4drv in its repositories.

I would have posted some links here, but GOG won't let me. Just head in the general direction of Github.

GOG will let you if you include a quote in your message. This is meant to combat spammers and the like but unfortunately wasn't well thought you.

You can quote this post and then put the link. Hell, even empty quotes work!

Accoding to github, ds4drv has not been updated for more than a year. I think sc-controller is nice alternative.