Why do different areas on a worksheet behave diffferently

I have a worksheet which at 80 rows and 290 columns is quite large
it is filled with a pivot table and then columns of formulae who's purpose is to sort and split this data into the form I need.
Because I wanted to keep the size of this sheet down, I had rows of formulae at the top of the sheet and these were copied and pasted down to the main part of the sheet, This was then copied and pasted to itself as values..
The problem started with the last copy and paste when nothing happened for several minutes until I got the " Not responding" message After some experimentation I discovered that given enough time the pasting of formulae and then values
did in fact work. I also discovered that little actions taking place in the "dodgy" area were very slow, like 3 minutes to delete a single character, whilst in the rest of the sheet though slower than usual the actions were OK.
I have tried copying a small part of the sheet to send with this post but none of my attempts have shown the problem. The following code is the sub that I use to do the copy and pasting. The various ranges that have to be set for this are all correct.

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I am not expecting a full answer, but I have never seen this before and would appreciate some indications as to what to look for. The slight slowness of the rest of the sheet could be due to the fact I am working on a remote device
through the internet.
John