Resaving Events Entries failed
There's only one entry named Transforming Work.


That might be true, but you’re telling Craft to store the entry with an URI

fort-collins/weekly/buddhist-meditation-classes/_entry


Change your entry URI format back to something that’s going to be unique for each entry, probably you’ll want to replace the hardcoded string _entry with the dynamic variable {slug} again, or better, do what is actually described in that Stack Exchange answer you linked to and don’t use the default Entry routing at all (disable “Entries in this section have their own URLs”) and rebuild the route with a custom one (see the Craft docs on Dynamic Routes).