Since UI7. Vera has provided a module,dkjson.lua, for encoding / decoding json. For over a year (since GCal R2.0). GCal checks to see if dkjson.lua exists and if so deletes json.lua. This was because, for many years GCal downloaded json.lua for UI5 because Vera did not always provide a module. Also, it was done to help minimize the amount of files stored on Vera as many users are short on space.
The correct fix would be for the author of OW to do the same test as GCal and use dkjson when on a Vera unit that has it. Can you please ask them and see what they say.