I am not sure how you have done the write operation. Any value can be written in to the GATT by locally (by same device itself) also using the same API CyBle_GattsWriteAttributeValue ().
When you will use write and write without response, you will get two separate events in the BLE call back stack event handler:
CYBLE_EVT_GATTS_WRITE_REQ: if using 'write' (write with response)
CYBLE_EVT_GATTS_WRITE_CMD_REQ: if using 'write without response'
On getting the above events (depending upon which option has enabled), call the CyBle_GattsWriteAttributeValue() API.
I did the write operation from my phone using the LightBlue Explorer App from my iPhone.
I have been calling CyBle_GattsWriteAttributeValue() in order to update the GATT database and that seems to work well.