Since the update to webthings.io, it is not possible for me to insert a custom symbol when editing the thing. After saving it is gone again. It cannot be found in the upload folder (/home/pi/.webthings/uploads/)
Thanks for reporting. This is a known bug that has already been fixed on master and should get fixed in the next bugfix release.
I’ve been waiting for a bugfix release for 7 months now, but I’m afraid nobody cares about this gateway anymore and obviously the wrong people got this great project.