!Update!
The Heroes of the Storm Dev team has just recently been able to reliably reproduce the issue and are working on the cause. This goes beyond the initial bug from late last year that affected most of Blizzard games and appears to be very specific to Windows based HOTS.
They have asked me to thank everyone that has sent in diagnostic files as they were extremely helpful in getting to this point.
The Dev team are currently testing new builds and will hopefully soon be able to release a fix.