Dell XPS 13 :: (L322X) Can No Longer Enter F2 Setup Screens / Graphics Diagnostics Error

Recently purchased the new i7 XPS 13 model (L322X). It's a lovely machine, but I have two problems with it.

Firstly, I can no longer enter the pre-boot setup screens. It did work originally, but now it simply doesn't load. I can still switch between different boot modes (Legacy BIOS mode, UEFI+SecureBoot, UEFI+No-SecureBoot) but I cannot actually get into the setup screens any longer.

If I switch to Legacy BIOS mode, then I do get text on the screen (bottom right) suggesting I can press F2. If I hit the key, the text changes colour slightly to suggest the keypress has been recognised, but then just proceeds to try and boot the machine (which fails as expected as there is no legacy bootloader).

Is there some kind of EFI variable that affects this - perhaps locking me out? I can still use the machine fine, but this is obviously disconcerting.

The second problem is manifested when I enter the Diagnostics utility in the EFI bootloader.

It reports all is well, except the Graphics:

It states:

Error Code: 2000-0332
Validation: 80763
Msg: Video memory - Video memory integrity test discrepancy

Please record the above Error and Validation codes

Further details are:
Vendor Name: uEFI
Product ID: Graphics Protocol
Vendor Version: N/A
VIDEO ADAPTER MEMORY TEST FAILED: 'Scan-test' AT LOCATION 0x3f00000
EXPECTED VALUE 0x0000000000000000 ACTUAL VALUE = 0x3030e6d8e977aa55
Test Results : Fail
Error Code 2000-0332
Validation 80763
Msg: Video memory - Video memory integrity test discrepancy