I found the problem with OpenSeizureDetector failing with Garmin Connect V4.31.
If you update to V0.9 of the GarminSD.prg watch app (https://github.com/OpenSeizureDetector/Garmin_SD/raw/master/WatchApp/GarminSD.prg), then it should work with all versions of Garmin Connect, so it is safe to upgrade Garmin Connect to the latest version.
For anyone interested the problem was a malformed url, so it should never have worked in the first place – I was sending data to http:127.0.0.1 but to be a valid url it should have been http://127.0.0.1. It is just that the previous versions of Garmin Connect were more forgiving and let me get away with it. It would have been nice for it to give us a ‘Malformed URL’ error rather than ERR-0, which means ‘Unknown Error’.
Sorry for the inconvenience!
Graham (graham@openseizuredetector.org.uk)