Be sure you are on the same version of Amazing Charts on all computers (there may have been a beta that came out at some point that had this messed up).
Also, be sure the computer clocks are set up so they appear the same. There are ways to adjust how the calendar is displayed, what day of the week is considered the first day, etc.
If you don't solve it, please let us know - as we should figure out what, exactly, is happening as it could imply a different issue, as yet unfound.
Just an FYI - most users don't experience any issue upgrading or migrating (though by the nature of the board, only those with issues tend to post - aka biased nature of reporting and the reason only positive studies tend to get published).