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.
You have another post here: https://portal.smartertools.com/community/a89059/reports-incomming-messages-freeze.aspx that I will also keep updated.