This happens with every composition.
whatever is causing it appears to be in the composition mapping
These statements are mutually exclusive. Something in the composition mapping cannot affect every compostion, unless you've previously saved it into every composition.
If you want to really debug whether or not it's something in the composition mapping, just save your comp and create a blank composition. If the problem still happens after that, the problem is not in your composition map.
Want to really debug if it's in application mapping? Go to the midi tab of the preferences, save your app midi map under a name you can remember and then create a new app midi map. Does this make the problem go away? Then the problem is in your app map.
Knowing you, I'm guessing you've got more than just one or two mappings assigned, which I'm guessing is also why you're ignoring the advice to remove all. The beauty of both these "debugging" techniques is that none of your previous work is lost. Both the comp map and the app midi map are safely stored and can easily be retrieved.
have you checked both deck and layer focus?
This is my guess as well. You've mapped something in one of the two, and thus far have only checked the other.
I've looked at the XML file but I can't seem to locate any column triggers
Which xml file have you looked at? Comp mappings are saved in the composition file. App mappings are saved in whatever app midi map you currently have loaded via the preferences. If you've never messed with this, it's saved in contextualMidiShortcuts.xml in your Resolume documents folder.
Either way, a column trigger can be found by searching for path="/track#1/connect". Where #1 is the column number the shortcut is assigned to.
But really, make sure you've checked both layer and deck focus in the app midi map before you start messing with xml files and the like. I'm 99% sure that's your problem.