version:latest curse, retail
(did not try only with dominos enabled yet)
started when 8.3 came out

Normally enabled positions for encounter bar and vehicle button:

Encounter bar appearing with sanity>

As soon as i am in combat, it moves to the middle of my character:

Not just for sanity, so far every time that bar gets used, solo, raid wherever.

(on a side note, also the exit vehicle button does not appear some cases it did before 8.3, but i did not made further tests yet)

Are you testing this with just Dominos + Dominos_Config?

said no, wanted to avoid turning on and off these 3000 addons one by one , but will not escape it.
so, after hours or turning things on off:
Seems that leatrix overwrites the dominos powerbar position in combat (if it is set to manage frames), turning off either leatrix frame management or dominos encounter fixes things.

vehicle button fixed as of now