Using: Excel 2013 64 bit

I have a relatively complex workbook open utilising multiple sheets, VBA, Tables and PowerPivot referencing those tables.

Because of the multi sheet structure it makes my life easier to have several windows open of this same workbook as it stops me needing to flick between sheets all the time. Potentially I will have twin views open of the same sheet.

What I have noticed, and what my issue is, is that often Excel will seem to freeze - sometimes I can navigate the sheet but simply can't select any cells or copy/paste. Other times the sheet is completely frozen. I can usually get temporary relief from the freezing by either (1) saving the workbook down or (2) switching to another sheet (in the same window) and then back again.

However, today this has not been working at all and I have found I need to close all the additional windows I have open and simply work from the one window (and I have not noticed this freezing occurring with only the one window open).

Does anyone have any ideas? My perception is that this problem has got worse over time - I use this spreadsheet each month and save it down as a new copy each month. The freezing is getting more frequent and to a greater degree of severity. It does appear to be cured by closing the additional windows though.

Thanks for any replies.