L76 - SBAS Problem

Hi. When SBAS support is on, my receiver will sometimes pinpoint the position to within 1 meter, and sometimes down to 3-5 meters. I have the impression that the longer it is on, the worse the results. When SBAS is turned off, there is no problem, rather I have a constant accuracy around 1-2 meters, does SBAS have any additional configuration? does the L76 module make a correction only from one SBAS that is, in its opinion, the most accurate? can SBAS give worse results?

Is it possible for the SBAS module to detect only one channel / sat with the one it considers most accurate?

If it matters, I have option GPS+GLONASS in PMTK353 mode.
Firmware ver: $PQVERNO,R,L76NR03A01S,2017/07/10,20

Dear sir

  1. Please check whether SBAS continues to participate in positioning during 3~5m?
  2. Please provide log data.
  3. Please try it with the latest firmware.
    L76NR04A01S.zip (1.2 MB)

Is there any documentation for the upgrade? I will have to implement sending the update myself because I have the module on the pcb, transmission only via uart. Have there been any SBAS fixes since my release? Thanks.

Dear sir
Please check the attachment, which contains the upgrade document and upgrade tool. Thanks!
FlashTool_exe_v4.1.0.zip (1.1 MB)

I cannot use .exe programs. I need to implement sending updates via uart. There is a possibility Eg. $PSTM sentence ? I am asking for documentation.

Please check the attachments, thanks!
Quectel_GNSS_FOTA_User_Guide_V1.0.pdf (179.7 KB)