Several of my regularly updated spreadsheets hang - always
on (auto-)saving, often
for no obvious reason. They are not large by 2010 standards, but contain a large-ish number of internal and external (to other spreadsheets) references and formulas. Many of the formulas call my own user-defined VBA functions.
Microsoft Support have tried twice and told me they had solved it - but also to no effect.
Apart from recording the timing of the save events, I can think of no way to diagnose where or how the problem occurs. I have considered external measures such as
adding more RAM OR
upgrading Excel to 2013 or 2016 OR
even upgrading Windows x64 from 7 to 10.
But they involve expense that may not be justified or may just add even more problems!