After the 1930 U.S. House of Representatives elections, newly elected members officially took office the following March but there was no active session of Congress until December 1931. Considering the ongoing Great Depression, why was there such a delay?
This was normal. Congress, especially "even numbered Congress" (the second half of a presidency"), met from December to the following summer. The assumption was the Congressmen would want to return to their farms for the harvest.
The Constitution, before the 20th amendment specifies that "The Congress shall assemble at least once in every Year, and such Meeting shall be on the first Monday in December, unless they shall by Law appoint a different Day."
Odd-numbered Congresses did sometimes have spring sessions, as needed by the President or Congress.
It changed in 1933 with he passing of the 20th amendment.