What is the problem with hosting encoding?

Question

PHP

Hello. Problem following: there is a script which generates a CSV file. The script contains a line like this:

$resultData = mb_convert_encoding($resultData, 'windows-1251');

If I run the script locally and open the resulting file via exel, then Cyrillic is displayed correctly.
I transfer the entire script to the hosting, run it there and get bugs (mostly question marks).
If you do not use this conversion function, then I get a normal string in UTF-8.
Tell me please, what could be the problem?
Thanks in advance to all who respond.

Answer 1

$resultData = mb_convert_encoding($resultData, 'Windows-1251', 'UTF-8');

I think the auto-detection of the encoding is glitched.