RasPi3B+ 3G/4G LTE Hat With Telit LE910C4-EU Stability Problem (Blue and Red LED frequently off)

Just received the Modem Kit, installation easy and OK with Raspberry Pi3B+. After this, USB driver downloaded from Telit, installed for Windows 10 OK. SIM card OK. But the device can be seen online only by WiFi, not LTE. And the blue LED (STAT) is sometimes ON then 5-10 seconds OFF quite randomly. And the bigger problem is the red LED (POWER) sometimes goes off too.
And this worries me because the power can not go just out. I changed to a USB power bank with 2.6 Ampere capability, still it goes off and on again. Measuring the voltage after the USB connector at the HAT is 4.9V. stable. So, it is not the USB cable, not power supply. The problem is probably on the HAT or the Modem module.
I am afraid I have to send it back…Thanks