Thanks for sending the sample log file across. I have now had a look at the problem and wanted to give you a quick update.
The issue is the the log file has some JSON like:
"message": "Petr's message."
The apostrophe in that message is causing a problem for our JSON parser as it needs to be escaped. This is creating a very clear, easily repeatable exception. I can also confirm that v2.5.14 does not have this issue.
What I have not yet been able to determine is - what has changed in the new version? As mentioned above, the JSON parser has not been updated between the releases, so It is a very strange error.
Unfortunately, I do not think this is going to be a quick fix. We will definitely fix this issue for the next release, but the next BETA release is still several weeks away. I will update this thread when a BETA release is available.
Thanks for reporting this issue!