Converted .xlsx to .csv and autofilter no longer works properly

I have an excel spreadsheet that was brutally slow when filtered (contained no formulas and all un-necessary formatting/rows/columns were removed)

I converted the file to .csv and it worked marvelously quickly once again and saved it back as .xlsx (still not sure why that worked, but I read it online, tried it, and had success).

Now when I filter for items I don't get expected results.

In this case I'm attempting to filter for anything containing "18.1"

I get all results that contain 18.1 delimited with another number or multiple numbers (18.1;15.2;15.6;etc..)

It will not return any results that only contain 18.1 (many exist in the spreadsheet).

Thoughts?

Thank you for that info...but it actually has now compounded to a different situation.

In my excel spreadsheet it will only count the 18.1s when they're delimited with another number if the cell is formatted as number

It will only count 18.1s when they're alone in a cell if the cell was formatted as text

If a cell with a single number has the green arrow in the corner alerting me that the cell is formatted as text and can be changed to a number it will be found by the filter if it is a single number. If a cell is formatted as number it will be found if it is delimited with other numbers.

I hope that makes sense.

It will also not work if I find an 18.1 that does not have the little green arrow and then try to right click and format it as text.