Apparently this is just a bug. If you enter year:xxxx and THEN other search terms (instead of putting year:xxxx at the end), it still works. Hopefully this bug can get fixed soon, but at least there is a workaround.
The search by year is available. If it's not working on your side, could you let us know what device, operating system and Spotify version you're using? Also, did this start happening after a specific update or event?
In the meantime, we recommend you give it a try on another device.
Hey @djisf!
This was reported and is being looked into. You can find all the info about it on this post.
If anything else comes up, don't hesitate to open a new thread.
Cheers.