I have a script that creates several files, each beginning with Zero Width No- Break Space ('EF BB BFX, BOM) and containing Hebrew text in UTF-8. When I open them in kate, some render correctly and some don’t. However, LibreOffice correctly renders a file that kate garbled.
You might narrow down the problem further by trying to create a problem in Kate and then again in another application, saving it and then opening in the other application to see if the problem is limited to creating or only reading the text, then submitting a bug to https://bugzilla.opensuse.org