My code to find longest string in column doesn't work properly! Need Help!!

Hi everyone,

i had a vba code that finds the longest string in a column and its location contains only "1"s.
It works at the sheet named "datasheet" (first sheet) but at the other sheets like "calc" and "charts" its useless.
What is the problem with this code? Additionally, i was having problem with the activating the sheet, it could be the reason?

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here is a example file of it.

example.xlsx

Thanks in advance