Resolved Plesk backup with message Encoding::encode: source UTF-8 encoding declared, but invalid UTF-8 sequence occured

[Bossman]

Created scheduled backups half year ago, backups are done each week, two weeks ago started to get such error:
"Encoding::encode: source UTF-8 encoding declared, but invalid UTF-8 sequence occured. Falling back to ISO-8859-1"

Found post about this problem, removed all files that where listed with grep.
That did not help

So found about debug mode in Plesk, but i am not sure how to do it properly. There are some questions....
I don't want to get out of space, it is production machine.

Anyone had such problem ?
Had solution for it ?

 

[Bossman]

This topic has been solved.
For anyone else, in my case it was domain which contained ó (polish char in name).