Calls to aci_gatt_update_char_value() return success but no notification is sent.

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I am looking for troubleshooting suggestions for a BLUENRG-MS with a STM32 processor. There are cases where calls to aci_gatt_update_char_value() return 0 but the client subscribed for notifications isn't receiving any. There are other code paths where this is working and I am looking for suggestions of things to examine.