Ok, I may need to have you send me the IPA so I can look at the signing bits in hex editor. However, I have a couple other ones in the queue to look at first. But, in the meantime, can you take the iPhonePackager.exe (UE4 4.9/Engine/Binaries/DotNET/IOS/IPhonePackager.exe) from 4.9 and replace the one in 4.10? Back up the one in 4.10 before replacing it. See if that works. If so, then it is 100% the new signing code for app distribution. Store off the current IPA for me to look at though 
-Pete
Can you try the attached iPhonePackager? Put it in 4.10InstallDir/Engine/Binaries/DotNET/IOS and then package as normal.
-Petelink text
Michael, if that one doesn’t work, I do have another fix that occurred later which resolved some problems with alignment issues in the requirements section. This could also fix your issue as the signature timeout could be related to a bad set up of the requirements. I have attached it here.
-Pete
I have tried both of the attached files, and both deploy the app to device successfully.
Thanks for all of your help!