Damir, I am working with Vecdi on a similar issue. I gave him a custom debug logging build which points us to the problem.  It has to do with the encoding in which the report JSON files were being read in.  I have since given Vecdi a custom build with the potential fix.  If you would like, I can also send the link to you. Regardless, I will update this post when our findings.

Damir, this issue has a confirmed fix.  It will be included in the SmarterMail 16.1 release tentatively scheduled for the end of the month.  If you would like a pre-release version which contains this fix, let me know and I can send you a link to the download.