Hello! We have been struggling with this issue for a while now and have isolated what might be causing the issues. Our suspicion is the combination of Raspberry Pi 3B+ and 4G dongle. We couldn't reproduce the problem with 3B model, using same SD card, same camera and same 4G dongle. It seems like the issue is with the 3B+. Take a look at these images:
With Raspberry Pi 3B:
With Raspberry Pi 3B+
One more example with Raspberry Pi 3B+
On the 3B+ model there are thick lines with color. And these lines do not appear after every boot. Sometimes in can take 5 hours for them to start appearing, but usually they appear soon after the boot (~5 minutes). Once they start appearing, they never go away, until the reboot.
We haven't tested with other model of 4G dongles, as we've been using the D-Link ones for a long time with the 3B model.
Has anyone experienced something similar with the camera? Any type of advice would be helpful.