SIM800L blinks three times

After power up, the modules (20% out of a batch of 50) blink three times, the only power led stays on for 30 seconds, module resets and 3 blinks per 30 seconds repeats.
The modules are used in an IOT environment and the other 80% work fine.
Any ideas how to get them started.

Hello and welcome!

How are you powering those modules? Which module are you using?

The modules are powered from the main power supply. There is nothing wrong with the power as replacing the module with another one instantly solves the problem.
The modules used are called
New SIM800L GPRS GSM Module w/PCB Antenne SIM Board Quad band voor Arduino
from aliexpress artikel
So far out of 100 modules 17 fail with the same symptoms.

Couldn’t find the specific module on aliexpress, is it one of these?

capture of some sim 800 modules

The one on the left is the module we have. We almost tried all 50 units and so far 21 of them failed.
Could the modules miss the required firmware?

Are you interfacing them with UART or something? To see if you get some kind of error or message that might help diagnose the problem.

If you get at least some of the expected functionality, I don’t think so. Even the fact that it blinks 3 times seems to show some kind of programmed logic. What seems more likely is that there might be some quality control issues on the soldering. Maybe some components don’t get properly soldered. I’ve used hundreds of the module on the right and have found 2 without solder on one of the sim card tray pins.