Was there Social Security fraud in Jonestown?

The short answer is no.

On 18 December 1978 — one month after the deaths in Jonestown — the U.S. Embassy in Guyana released a list of 656 uncashed government checks that were recovered from the jungle community site. The Embassy compilation — including the check numbers, their date of issuance, the names and Social Security numbers of their recipients, the check amounts, and their designation as Social Security benefits — was reprinted in The Assassination of Representative Leo J. Ryan and the Jonestown, Guyana Tragedy, the May 1979 report of the Staff Investigative Group of the House Foreign Affairs Committee.

An analysis of those checks conducted in 2002 by the editors of this website found that, contrary to reports published after the deaths in Jonestown in November 1978, there was little (if any) fraud involving Social Security recipients or benefits.

The complete report is here.