RC7620 (FW 8.07): "AT+KSLEEP=2" command does not seem to work correctly

Hi Guys,
I want to execute the “AT+KSLEEP=2” command to disable sleep mode for UART1. UART1 sleep mode is disabled for the current session only. Although the “AT+KSLEEP=2” command does keep its state after a power cycle UART1 still falls asleep. Only repeated command “AT+KSLEEP=1” followed by “AT+KSLEEP=2” helps. But after the power cycle, the sleep mode turns on again. For comparison, I also have HL7692 - everything works correctly there.
Below is the report. Please advice. Thanks in advance!

AT+KSLEEP=2 //enter no sleep mode (regardless of DTR state)
AT+KSLEEP=2 
OK		   //the command completed successfully
AT+KSLEEP? //status check
AT+KSLEEP?
+KSLEEP: 2 //the UART1 state saved correctly

OK
AT!RESET //reboot
AT!RESET
OK

+SIM: 1 //modem started


+KTCP_NOTIF: 1,5

AT //the commands are sent at intervals of more than 5 seconds - no response
AT //UART1 is sleeping
AT //UART1 is sleeping
AT //
OK //UART1 wakes up after the command (<5sec)
AT+KSLEEP? //status check
AT+KSLEEP?
+KSLEEP: 2 //state saved correctly but UART1 is sleeping

OK
AT+KSLEEP=1 // reset-set helps, but only in the current session
AT+KSLEEP=1
OK
AT+KSLEEP=2
AT+KSLEEP=2
OK

AT //the commands are sent at intervals of more than 5 seconds, the modem is responding
OK //UART1 is not sleeping
AT
OK //UART1 is not sleeping
AT
OK //UART1 is not sleeping
AT
OK //UART1 is not sleeping
AT!RESET //reboot
AT!RESET
OK	//After reboot UART1 goes to sleep again

+SIM: 1 //modem started


+KTCP_NOTIF: 1,5

AT
AT
OK
ATI
Manufacturer: Sierra Wireless, Incorporated
Model: RC7620
Revision: SWI9X07H_00.08.07.00 0ce4c1 jenkins 2021/03/17 02:18:20
IMEI: 353634110241543
IMEI SV: 17
FSN: 7Q1385310310B0
+GCAP: +CGSM

OK

This is known issue with internal tracker MOLRC9X07-89.
You need to use your workaround to overcome this issue at this stage.

This work around works for me on the RC7620 with firmware version 00.08.07.00.
Thanks help9help.

I did not have this issue with firmware version 00.03.03.00.

However, before going into MUX mode, it was also required to toggle the DTR pin for 100ms.
Otherwise a channel (DLC) could not be opened.