I checked inside the mod, in the specific folder are only arithmetic-combinator-frozen.png and decider-combinator-frozen.png
Why it is searching for the selector version i cant say but the error on itself is not wrong, the file is "missing"
Edit: Now i get it, i think they added in .20 a frozen version of the selector which maybe did not exist before.
(Factorio\data\space-age\graphics\entity\frozen\combinator -> found a selector-combinator-frozen.png in the gamefiles)