Not sure if there is or was size limit (in past people used to host +300MB packs externally)

If no limit than maybe you bricket something with constant uploads +same Sona.1.var package (looking at history tab).
instead of "post update" did you try "change resource type" option and upload there?
or maybe create new update/version package (...Sona.2.var)
or delete some of those "bad" uploads (in history tab)
EDIT: apparently there was 100MB limit and now it's 500MB
It appears you are trying to update with same version 1 package or completely new package but still as "version 1", if that makes sense.