First, if you are on MC20.0.131 you should update to MC20.0.133 as there were a few fixes in the last two updates of MC20. See
https://wiki.jriver.com/index.php/Release_Notes_MC20The XMLTV format hasn't changed. What are you using as the source of your data?
I'm not at my TV setup right now, but if you have valid XMLTV data being collected and it is up to date, then does a Manual Load of program guide data work?
If not have a look at the setup of the load process. Maybe something broke and just editing and saving the changes will fix it, or you may need to do a little re-setup.