EG25-G does not enter sleep mode

I am facing a problem where I am unable to put the module into sleep mode. Please support me.
I am trying to set up a system where the host and EG25-G are connected via USB communication and I want to put EG25-G into sleep mode.
EG25-G’s “DTR” and “WAKEUP_IN” are always open.

I tried to put EG25-G into sleep mode by the following procedure, but it does not seem to be in sleep mode.
(1) After EG25-G starts up, send AT command “AT+QSCLK=1” from the host to EG25-G via USB.
(2) Disconnect “USB_VBUS” of EG25-G from the host.

To confirm that the device is in sleep mode, monitor the current value of VBAT.
At the stage when (1) was completed, VBAT was about 45mA in Idle state. At the stage when (2) was completed, VBAT was about 40mA.
I believe the 5mA decrease is due to the current consumption of the USB block in the EG25-G.
I am hoping that after (2) the current will be less than 5mA if the device is in sleep mode.

Please support me on the following
What could prevent the EG25-G from going into sleep mode?
Is there any way to explicitly know that the EG25-G is in sleep mode other than the current value?

The above matter is now self-resolved. Thank you.
Though I had GNSS ON (AT+QGPS=1) in (1) startup, I was able to enter sleep mode by turning GNSS OFF (AT+QGPSEND) before entering sleep mode in (2).
This is a consequential question, but is it a necessary control to turn off GNSS before entering sleep mode?
And is there a statement in the datasheet that it is not possible to enter sleep mode when GNSS is ON?