As I have seen no answers, I think this problem is still not solved. I am just flying from Frankfurt (EDDF) to New Doha (OTHH) and close before reaching TOC, ATC diappeared. I still can hear ATC, but I cannot choose any items in the ATC window menu, they are all gone.
If anyone reads this topic and knows a solution, is welcomed to reply. And.. yes.. this happens very rarely, but it does happen once in a while.
Achim