I just logged back in and saw my refund amount decrease by about 20%, even though no changes have been made from the last time I saved. Any ideas why this would happen?

There may have been a program update.  Updates come out on Thursdays.  Or you entered something that affected it.  You should not watch the Refund monitor until you are done entering everything.

Is there a place to view how a "program update" can make such a drastic impact?  Again, nothing was entered between what the refund showed between the two points in time.  Everything was already entered, so there was nothing to update.