It sounds like a firewall issue, from your description (such as the firewall not recognizing Tixati any more after the upgrade, and hence a new exception needing to be added, or a change of port requiring to make sure that the new ports are properly forwarded), and I would start there.
Anyway, if needed you can revert by simply installing the older version over the newer one as stated, it will work just like the inverse way and all your settings and torrents should be kept.
If you can't find a direct link to the version you want to download, you can simply edit the current download link. For example:
Replace:
http://download1.tixati.com/download/tixati-2.34-1.win64-install.exe
With:
http://download1.tixati.com/download/tixati-2.31-1.win64-install.exe