GPRS services resumption issues after PS Redirection from LTE to GSM after activation of MLB to GERAN

3G / 2G
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1

Hi Experts.

I am observing GPRS services resumption issues after PS Redirection from LTE to GSM after activation of MLB to GERAN. This channel release message is immediately received after Location Updating Accept and TMSI Reallocation Complete.
My Questions:

  1. Why it’s doing location updating procedures where in CSFB in same location, there is no location update due to combined attached? Or why it’s essential to perform TMSI reallocation?
  2. After Channel Release, there is Rauting Area Update and Immediate Assignment (TBF Allocation) due Application based session re-attempts. But It also shifts to LTE due to fast reselection to LTE. As the TBF is allocated again why Fast Redirection is pushing the 2G GPRS sessions to LTE?
    -Vendor: Huawei
    -NW: LTE/2G only
    -TA/LA mapped and Combined TA/LA Update is active.

Reference:

Channel Release
L3SM	GSM	Downlink	2022-8-20 16:27:52.143	DCCH	CHANNEL_RELEASE		
CHANNEL RELEASE		3GPP TS 44.018 ver 13.4.0 Rel 13    (9.1.7)

M Protocol Discriminator (hex data: 6)
	(0x6) Radio resource management message
M Skip Indicator (hex data: 0)
	Value: 0
M Message Type (hex data: 0d)
	Message number: 13
M RR Cause (hex data: 00)
	RR Cause value (0): Normal event
O GPRS Resumption (hex data: c0)
	Resumption of GPRS services not successfully acknowledged