I figured it out, and am quite embarrassed. At some point while making changes I managed to copy one of my gateway scripts, in its entirety, to the end of an unused function at the bottom one of my project library files. This included the import json statement.
The library was the source of the error which wasn't evident by the contents of the log's traceback. Thankfully the Gateway Scripts tab pointed to the issue more directly. Thanks for taking the time to help, and sorry for the inconvenience. I'll be more thorough next time.