I have written some code that imports text files, for each file a new worksheet is created.

If I just use 
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then Excel starts behaving erratically after adding about 20 sheets. By erratically I mean, freezes, sometimes the code runs, sometimes the code doesn't.

If I use 
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the code is much more stable, but still crashes after adding lots of sheets (100+)

The sheets don't contain huge amounts of data (range"A1:G2000")

The very same code runs without any issue in Excel 2007.

The second issue is using find and replace;

Using the worksheets with data in the range A1:G2000 and using find and replace takes a long time.

I have tried limiting the search range by specifying a range (A1:A2000) instead of using a column reference (Column A) which sometimes speeds up the process but not always.

The data is just long strings of text (123desfadsf9asdfas7dfa9sdf9a8sd9f8898asdf)
Running the exact same code in Excel 2007 and it runs across 500 worksheets in less than a minute, using Excel 2016 it takes 10 minutes, sometimes much longer. I have set calculation and screenupdating off but this does little to speed up the code, in fact, with screenupdating on the code runs without any issues, other than being slow with screenupdating off Excel 2016 hangs and more often than not crashes.

Any ideas on how I can attempt to fix these issues?