A few months ago I had updated from 2.4 to 2.5 on my Raspberry Pi 3 (Openhabian distro) and my icons in the Eclipse SmartHome Classic iconset disappeared. After searching for a while I found Kai’s solution and solved the issue:
Yesterday (after a few weeks of not applying updates) I decided to update the 17 pending items in the queue, and after the update finished icons were gone once again.
I bookmarked the fix in case it happens again in the future.