Hi,
I’m using “still” in the title because these icons were already missing in the previous beta versions:
Hi AnneSchmidt,
I can’t reproduce this issue. Did you already file a bug report for it?
No; nobody never manage to reproduce the issues I report, so… These materials were created with an earlier version; I’ll try and remake them.
Okay, just made a new material and this time the icon is there; I suppose the problem was fixed in an earlier version and I didn’t notice. I don’t understand why the others are not there though.
Usually reimporting them fixes the issue. If you had imported a project from an earlier version it’s best to reimport all assets.
Not sure about reimporting assets I made but I also got a bunch of error messages in the console about timestamps and GUID mapper that weren’t right. I deleted the “Library” directory and all the meta files, reloaded the project and the error messages have disappeared. 
You don’t refer to those .meta files that exist next to each asset, do you? Because Unity uses them to reference and identify assets, as well as save asset import settings. They contain quite some important information.
Yes, they are recreated as soon as you relaunch the project; after that I had to reaffect the assets to the object they were attached to but it’s a small project so I took the risk