I've noticed from time to time that data isn't uploaded anymore.
A reboot of the meter helps, but of course, all data that wasn't uploaded is lost.
Last weekend, i've did some tests, and saw that when you simple remove the antenna, and put it back, it works again. So this without losing the data.
I've put the antenna now in direct line with the access point. Distance is about 10m...
Maybe it was an interference with the electrical cables?