I cant even run my keys so I feel ur pain. stupid updates

Same thing happened to me, and another member in my clan. Got the rewards for brutal and nightmare, but not for ultra nightmare. I'm playing on an ipad8. Must be a common bug after the update, and I hope they fix it quickly.

The rewards have arrived. It was just a delay on the unm rewards.

Still don't have UNM reward chests.  Got every other chest but that one as well.

Here is a potential solution for Windows users from the official Discord. 

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If you are playing on Windows and you have been experiencing issues with Clan boss rewards and/or Battle button being "greyed out", please install the followings:

Windows update - KB3063858
64-bit https://www.microsoft.com/download/details.aspx?id=47409
32-bit -  https://www.microsoft.com/download/details.aspx?id=47442

C++ 2015-2019 Redistributable
64-bit - https://aka.ms/vs/16/release/vc_redist.x64.exe
32-bit - https://aka.ms/vs/16/release/vc_redist.x86.exe

I have also heard that running a key lets you get the prior days rewards, but still compiling information on that.

For those who don't receive rewards regardless, please open a support ticket.