MF286D, modem sometimes connect to 3G only

Dear All
Thank you for you support
I have MF286D with latest stable OpenWrt and B12 modem
Some times the connection default to 3G (WCDMA 2100) with green led flashing , the only way to have 4G again is power restart
I hope someone could help me with this problem
thank you all
Manufacturer: ZTE CORPORATION
Model: MF286DMODULE
Revision: BD_TELIAMF286DV1.0.0B12
SVN: 12
IMEI: XXXXXXXXXXXXXXX
+GCAP: +CGSM,+DS,+ES

Please post output of

ubus call system board

command

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root@OpenWrt:~# ubus call system board
{
        "kernel": "5.10.201",
        "hostname": "OpenWrt",
        "system": "ARMv7 Processor rev 5 (v7l)",
        "model": "ZTE MF286D",
        "board_name": "zte,mf286d",
        "rootfs_type": "squashfs",
        "release": {
                "distribution": "OpenWrt",
                "version": "22.03.6",
                "revision": "r20265-f85a79bcb4",
                "target": "ipq40xx/generic",
                "description": "OpenWrt 22.03.6 r20265-f85a79bcb4"
        }
}

Upgrade the router firmware to the latest.
Connect to the modem from a terminal like picocom and query it with the following commands:

AT+ZSNT?
AT+ZNLOCKBAND?

Post the results. There is no need in posting pictures.

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So it does not default to 3g, please adjust the title

Data band select..

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Thanks, I mainly have band 3 and 32

AT+ZSNT?
+ZSNT: 1,0,0

AT+ZNLOCKBAND?
+ZNLOCKBAND: 88000004,2000000680380

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Set AT+ZSNT=6,0,0
If you want to keep 3 and 32 only, then you need to use 80000004 mask.

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Thanks
Is this the right AT command?

AT+ZNLOCKBAND=1,0,80000004,0

Correct.
AT+ZNLOCKBAND=<lte_band_enable>,<gw_band_enable>,<lte_band_mask>,<gw_band_mask>

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Now I get


AT+ZNLOCKBAND?
+ZNLOCKBAND: 80000004,2000000680380

OK

That's fine.
Check with AT+ZCELLINFO?
Note if B3 is [temporary] not available, you will not be able to connect at all.
I suggest adding other bands if they are available on the same tower.

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AT+ZCELLINFO?
+ZCELLINFO: 13493250, 149, LTE B3, 1392

OK
thank you so much AndrewZ
I will keep eye on it and update the post

Is there an AT command to reset the modem saved settings to factory defaults?
another question can I downgrade the modem firmware?

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