And the answer is...
At some point in the past, the project had been edited to include a local copy of the msbuild folder and I had forgotten about it. I used sysinternals' procmon to find the file access and it was only referencing msbuild under my project.
With that, i renamed the folder, edited the csproj file to remove the localized references for the MSBuildExtensionsPath32, and reloaded the project.
I was able to successfully publish my app.