EM7455 unexpected reset after few hours of work

We experience problem with one specific box, having EM7455 modem.
After few hours of uptime (sometimes 4h, then 2h etc), modem gets reset (based on uptime of AT!gstatus?).
Reason for sure is not inactivity, as we have each second ICMP traffic via the modem.
Control software on the box doesn’t reset it , what can reset it ?
Can poor radio signal or Operator make it reset ?
Few other boxes with same setup don’t have this problem.

SW: Linux 4.18.0-21, Drivers: qmi_wwan , cdc_wdm
Operator: AT&T

ati
Manufacturer: Sierra Wireless, Incorporated
Model: EM7455
Revision: SWI9X30C_02.24.05.06 r7040 CARMD-EV-FRMWR2 2017/05/19 06:23:09
MEID: 35907306231601
IMEI: 359073062316017
IMEI SV: 12
FSN: LF903586140210
+GCAP: +CGSM

AT+GMR
SWI9X30C_02.24.05.06 r7040 CARMD-EV-FRMWR2 2017/05/19 06:23:09
AT!IMPREF?
!IMPREF:
preferred fw version: 02.24.05.06
preferred carrier name: ATT
preferred config name: ATT_002.027_000
current fw version: 02.24.05.06
current carrier name: ATT
current config name: ATT_002.027_000

AT!gstatus?
!GSTATUS:
Current Time: 35751 Temperature: 37
Reset Counter: 11 Mode: ONLINE
System mode: LTE PS state: Not attached
LTE band: B2 LTE bw: 15 MHz
LTE Rx chan: 775 LTE Tx chan: 18775
LTE CA state: NOT ASSIGNED
EMM state: Reg Initiated Waiting for NW
RRC state: RRC Connected
IMS reg state: No Srv

PCC RxM RSSI: -78 RSRP (dBm): -101
PCC RxD RSSI: -75 RSRP (dBm): -96
Tx Power: -2 TAC: 8749 (34633)
RSRQ (dB): -15.1 Cell ID: 0B9653DB (194401243)
SINR (dB): 16.8

No.

did you check for a crashdump?
at!gcdump

  • modem powercycle will clear gcdump, modem reset will not

reset could be power related too.