Comment # 14 on bug 1175487 from Sean O'Connell

I have done further testing on this issue and have isolated the problem to
interaction with the 'async' package (https://github.com/jwiegley/emacs-async).

There are two async package versions currently available:

async 1.9.3 (gnu)
async 20200809.501 (melpa)

I have tested the Emacs packages from the TW repo, from the Editors repo, and
from Andreas Schwab's Emacs repo.

Andreas' build has no issue with either async package (gnu or melpa).

The builds from TW and Editors both present the "error in process sentinel:
async-handle-result.." error once either async package (gnu or melpa) is loaded
and a network file download operation is performed (e.g. installing a package
or downloading an enclosure in Elfeed).