I only found the following at the Nobel Prize webpage:
Why were the Nobel Prizes not awarded in those years? In the statutes of the Nobel Foundation it says: "If none of the works under consideration is found to be of the importance indicated in the first paragraph, the prize money shall be reserved until the following year. If, even then, the prize cannot be awarded, the amount shall be added to the Foundation's restricted funds." During World War I and II, fewer Nobel Prizes were awarded.
which does not says much. In 1916, 1940-42 it is quite reasonable to assume that there was no awarding due to the world wars. But then, what about 31 and 34? Of course there were many contributions to physics which where achieved in the preceding years and that could have been awarded.