Here's the already fixed files including the code from Droider's original post.
Locations:
\Demonbuddy\Plugins\QuestTools\UI\PercentConverter.cs
\Demonbuddy\Plugins\QuestTools\ProfileTags\CompleteGreaterRift.cs
These are modified from Quest Tools v. 2.1.36 so make sure you're on that version as I'm not sure if there were any changes from the version before.
Tested and confirmed it is working.