I've found a glitch in my D750 which is probably firmware based, but is not a major inconvenience for me and my uses.
When using the AF-S TC-20E II 2X Teleconverter, the time-outs for image playback and menus stop working, they just stay on until you press the shutter button (before release).
I checked to see if my time-out preferences had been corrupted and they are as I had them set, and when the teleconverter is removed, the time-outs return to proper function. Don't know if this is also a problem with other models of the TC-20 or the 1.7 teleconverter, or just mine (contacts are pristine). One person replied to me that there was no problem like this with his TC 1.7converter.
I should also note that in addition to the display time-out issue, AF didn't work with the TC-20E II attached. It did work with my D600, and the D750 has otherwise superior AF, so it seems it should have worked in the same settings. I'm aware of the more limited f/5.6 and higher focus point construction of the D750, so I may have to find a specific AF and focus group setting to get it to work? I only use the TC-20E II with the AF-S 300mm f/4D, and both were seated properly.