I’ve just experienced this problem doing a Replace All.
I have a csv file (not yet saved) with 164000 rows in it. I did a Replace All changing n with ,n (added a column to the end of the data row).
A popup appeared with a check box ‘Accelerate by Discarding Undo Information’ which I ticked. The action took minutes to complete !!! Previous versions used to run significantly quicker.
The ‘Additional Lines to Search for Regular Expressions’ is set to 0.
I ran the Replace All again with the same criteria and it took just as long.
I ran a third Replace All changing ,, to , and the process took less than a second.
The problem would seem to be related to regular expressions.
Is there any way of disabling the undo during a Replace permanently ?