Actually 5G Icon appears in your phone due to LTE SIB2 that include UpperLayerIndication-r15 IE flag that supposed to be “1” . So this scenario is likely occurring because of 5G icon shows it is just configuration issue.
The GSM Association (GSMA) has agreed upon a set of 4 candidate UE configurations which determine when a UE should display the 5G icon. These 4 configurations are presented in Table (this config is depends on UE manufacture vendor).
configuration ‘A’ is the most conservative because it limits the UE to displaying the 5G icon when the UE is already connected to both LTE and NR cells.
In contrast, Configuration ‘D’ is the most aggressive because it allows the UE to display the 5G icon when using only an LTE cell belonging to an NSA Base Station, without having to verify NR coverage.
Configurations ‘B’ and ‘C’ rely upon the UE verifying that NR coverage exists
Solution: some vendor have setting for UpperLayerIndicationSwitch that may configure so let LTE SIB2 broadcast upperlayerindication-r15 only if E-UTRAN cell is configured with at least one neighboring NRCell.
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