Some validators says you put invalid tags in XML sitemap

https://www.mysitemapgenerator.com/service/check.html

Error:

"All values in a Sitemap must be entity-escaped. Please check to make sure that your URLs follow the RFC-3986 standard for URIs, the RFC-3987 standard for IRIs, and the XML standard."

https://odzyskiwaniedanych.net.pl/tag/odzyskiwanie+danych

I also think you should trim out the priority to 2-3 places after period

<url>
<loc>https://odzyskiwaniedanych.net.pl/tag/arkusz+kalkulacyjny</loc>
<priority>0.33333333333333</priority>
</url>