There's no way we can analyze your spreadsheet until you upload a copy of it, as Zizi64 has already requested.
If you're getting #DIV/0! then Calc is seeing 0 numbers for the division portion of the calculation needed to obtain the average.
Since COUNT is giving you a blank cell, which (probably) means that you have the display of 0 value cells disabled, what do you get if you use the same range, but the COUNTA function?
This will tell you how many non-numeric entries Calc is recognizing.
If you have numbers that have been imported or entered like text, then the removal of the formats will not make any difference, with the (possible) exception of the alignment.
See
How to attach a document for assistance in uploading/attaching your document.
OpenOffice 4.1.7, LibreOffice 7.0.1.2 on Windows 7 Pro, Ultimate & Windows 10 Home (2004)
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