Did this change recently?
font.export(FontPath=vf_path, Format=VARIABLE, Containers=[PLAIN, WOFF2], AutoHint=False)
only generates a TTF and font.export(FontPath=vf_path, Format=VARIABLE, Containers=["PLAIN", "WOFF2"], AutoHint=False)
generates a TTF and a WOFF but not a WOFF2