Here's another Freebox Revolution related issue. My seeding torrents were not classified as such, they showed an empty bar even though they're at 100% and not info about upload speed. So I tried to find out why, had a look at the JSON data sent by my transmission daemon and saw it reported a status code 8 instead of the 6 your code is expecting. Changing from a 6 to an 8 in the extension code fixed the issue.
It seems the Freebox is running an old Transmission version and the codes changed since.
Here's another Freebox Revolution related issue. My seeding torrents were not classified as such, they showed an empty bar even though they're at 100% and not info about upload speed. So I tried to find out why, had a look at the JSON data sent by my transmission daemon and saw it reported a status code 8 instead of the 6 your code is expecting. Changing from a 6 to an 8 in the extension code fixed the issue.
It seems the Freebox is running an old Transmission version and the codes changed since.
I dug further and found https://forum.transmissionbt.com/viewtopic.php?f=1&t=13357 with a similar issue, which links to https://github.com/killemov/Shift/blob/master/shift.js#L676 where you can see a way to handle both the old and new codes.
Using this code as a library might be the best way to avoid further issues, but maybe this is too heavy for your extension.