Fiendish Resilience (Warlock, Fiend, PHB 109) damage resistance type appears to not be selectable anywhere on the character sheet or on rest.  

The deprecated Noble Genie UA was able to select Elemental Resistance type in the character editor but not on the sheet, so the UA actually had better functionality.

Is this a bug or a missing UI element?

A fix would be appreciated!  If players have to manually edit their resistance every time they want to change it, new players won't realize they have it and others will likely forget and/or have to say "well I would have . . .", which wastes time and puts extra strain on the game.  Thanks for any help!

I think they are saying that because the genie works properly, the Fiend should as well. They aren’t claiming that the genie doesn’t work.

Quote from GPyromania >>

Thanks for the heads up regarding Fiend Warlocks - I’ve passed this along to the team.

Secondly - can you elaborate on with regards to the issue with The Genie subclass? As far as I can tell, it functions correctly in that it properly provides the resistance specific to the Genie that you selected at level 1.

Thanks for your attention on this!  Much appreciated.
I don't see anything wrong with The Genie Warlocks - as I said, I was referring to the functionality of the (now deprecated) "Noble Genie UA", which were able to choose an elemental resist on long rest which they could temporarily activate and share.

Quote from GPyromania >>

I understand what you mean - the reason why this was "deprecated" is because while the UA material allowed you to change your elemental resistance after a long rest, the official version from Tasha's Cauldron of Everything specifically requires you to choose your genie patron (and therefore your resistance) at level 1. D&D Beyond always strives to reflect the rules as accurately as possible - and in this case we defer to the official content in its implementation. 

 Oh certainly - I'm not in any way requesting support for obsolete UA material, I'm just using it to make a comparison about functionality.  When I use the word deprecated, I'm using it in the common programming sense . . . a feature that still exists but is no longer used.  That's what Noble Genie is (character sheets containing it can still be used, but new ones cannot be made).

That's why I used present tense for Fiendish Resilience, and past tense for Elemental Resistance.  I'll try to be more clear in the future.

I levelled up my warlock yesterday and encountered the same problem.

Will there be a resilience  select box in the future or will it stay like this?