As far as I am aware, Bluetooth transfer speeds in general are somewhat low compared to other wireless network protocols such as Wi-Fi. And the transfer speeds can vary greatly between devices depending on the Bluetooth chipset and its capabilities of each device, network interference, distance etc. So I highly doubt it is a software bug.
If data transfer speed is a concern, then I would highly recommend you to use another transport protocol such as Wi-Fi and only keep Bluetooth for establishing the initial connection.