What the logcat shows. Like:
E/RILQ ( 1071): (0/1071): RIL[0][rild] qcril_log_init: Fail to initialize Diag for QCRIL logging

E/RILQ ( 1071): (0/1071): RIL[0][main] qcril_qmi_init_core_client_handles: qcril_qmi_presence_init returned failure(31)
E/RILQ ( 1071): (0/1071): RIL[0][main] qcril_qmi_nas_retrieve_custom_emergency_numbers_co nfigured_value: Invalid value for properties count 0
E/RILQ ( 1071): (0/1071): RIL[0][main] qcril_sms_perform_transport_layer_info_initializat ion: error while retrieving transport layer reg info
E/RILQ ( 1071): (0/1071): RIL[0] get_ecc_property_name: ecc list name : ril.ecclist.

E/RILQ ( 1071): (0/1071): RIL[0][event] qcril_uim_update_pbm_card_event: PBM_HANDLE_CARD 397313 processing Failed!
E/RILQ ( 1071): (0/1071): RIL[0][event] qcril_uim_update_pbm_card_event: PBM_HANDLE_CARD 397314 processing Failed!

I am not sure whether this is connected the issue with the mobile data.


Edit: This was a red herring as these are not errors.