Thought I had it!
Renamed the JSON file to ‘group_5746a271a9731.json’ to match the Field Group key.
But still no luck. Verified Read/Write permissions for all on both the acf-json directory and the JSON file.
Interestingly, note the suggested title for the Rule Group to sync DOES seem to have a group-key as part of the title, but it is different from any key in the JSON file, AND is different each time I reload the page.
