I’ve also added a few zeroes to the max upload size even though it shouldn’t have been necessary. As mentioned, it seems to fail from 1MB upwards.
The upload dialog appears, it appears to upload and to finish and then “an error occurred” if the file is larger than 1MB:
My main question: How would you debug something like this? If there is code that makes the error message appear doesn’t that code log that error somewhere?! Perhaps with a more helpful error message.