It seems that the AL extension updated for me this morning and now I have this weird bug where it complains constantly about the fact that "AppSourceCop.json" is missing this property... that does not belong to this file.
Notes:
Ok: I had just posted a comment saying that it had stopped happening, but I deleted it because I've found out what triggers the error: editing the AppSourceCop.json file. The error/warning appears as long as the file is open in VS Code, but disappears as soon as you close it.
Thanks @salgiza ! This sounds like a bug. I will take a look into it. What is the error code of the diagnostic you are getting?
I don't actually get any error code, this is the message I get in the "Problems" console:

I understand. We'll fix it and push out an update. Thank you for the feedback!
The fix for this issue has been checked in to the master branch. It will be available in the bcinsider.azurecr.io/bcsandbox-master Docker image starting from platform build number 38464.
If you don鈥檛 have access to these images you need to become part of the Ready2Go program: aka.ms/readytogo
For more details on code branches and docker images please read:
https://blogs.msdn.microsoft.com/nav/2018/05/03/al-developer-previews-multiple-releases-and-github/
https://blogs.msdn.microsoft.com/freddyk/2018/04/16/which-docker-image-is-the-right-for-you/
Most helpful comment
I understand. We'll fix it and push out an update. Thank you for the feedback!