I've has issues when installing versions in the past where I couldn't get into the web interface. Unfortunately, I had to uninstall the tvheadend addons...and make sure to delete the userdata files as well. When you uninstall through kodi - it doesn't delete your settings...so you have to do that manually to get a clean install.
Definitely check the epg source list for multiple versions of the same channel first. If there are more than one - select all the versions that have the correct channel number/name. You only need the one that is the "right" one - but it's easiest to select them all for now and see if that gets things working.