EC200U-EUAA Antenna problem

I have three EC200U models: EC200U-CN-AA, EC200U-CN-LA, and EC200U-EU-AA. As far as I found, EC200U-XX-AX means the device supports both 2G and 4G, and EC200U-XX-LX means the device only supports 4G.
I have soldered all models on the same PCB design and found problems in LTE antenna performance in EC200-XX-AX models. The AA models (CN-AA and EU-AA) both connect to the network with 12~15 signal strength while the LA model connects with a full antenna (30~31). I used the same external antenna at the same place for all the modules.
Both EC200U-XX-AA models have GNSS functionality as well and I wonder if it is related to the GNSS RF or not.
I also have disabled the internal GNSS, but nothing changed.
What could lead to the problem and how can I solve it?

Hi
I will answer your questions very enthusiastically. As you said, the -AA module supports 2G and 4G networks, so I suspect that your module is registered with 2G networks first. Please enter the AT command through the usb AT port, at+creg? AT+CEREG? AT+CGREG? To view the network registered by the module.
Beat wishes

Hi,
In some cases, at the start, it registers to the 2G network and after about 10 seconds it connects to the LTE network. But in most cases, it connects to the LTE network from the beginning.
I can see more details using “AT+QCELLINFO?”
+QCELLINFO: “servingcell”,“LTE”,,,,,,20,170,100,-120,-90,47
+QCELLINFO: “neighbourcell”,“LTE”,
,**,
,,410,21,-,1800,-,-,-
+QCELLINFO: “neighbourcell”,“LTE”,
,**,
,,54,18,-,1800,-,-,-
+QCELLINFO: “neighbourcell”,“LTE”,
,**,
,******,54,11,-,2850,-,-,-

“AT+CSQ” returns “+CSQ: 12,99”

AT+QENG=“servingcell”

+QENG: “servingcell”,“NOCONN”,“LTE”,“FDD”,,,***,**,2850,7,5,5,,-123,-15,-89,43,2

OK
AT+QENG=“neighbourcell”

+QENG: “neighbourcell intra”,“LTE”,100,54,-121,-12,-,-,4,-,-,-,-

OK

Hi
Have you checked what network the modules with poor signal quality are indicating? If so, please check if it is the reason above
Best wishes

Hi,
As I showed before, the module(EC200U-CN-AA and EC200U-EU-AA) is now connected to an LTE network with poor signal quality (+CSQ: 12,99).
I soldered an EC200U-CN-LA module (only 4G) to the same PCB and it registered to the same LTE network in the same position with the same antenna and the connection is good (+CSQ: 31,99).
Any help in debugging the case is appreciated.

A small footprint error in the uFL connector was the reason behind it.