I noticed that navigraph charts desktop app was also not loading either and at that point I have discovered I've had a network issue. I restarted network connection and the map buttons are shown once again. However it appears that the map cannot recover from this situation once connectivity is restored.
OIS Enroute map started off fine but after a while map tiles have stopped loading and all map controls are hidden and all I'm left with is a blank screen. EFB charts also exhibit same issue.