I have not owned or working on a D5 like yours, but I experienced that thing with my work for some customers. Bluetooth Wireless Apple Carplay or BLUETOOTH alone and IPhone seem having something funny with setting and firmware. Check to see what iOS firmware you have, and try to do Network Settings Reset. Unfortunately, this issue belongs to iOS and a right firmware with right settings will likely fix it. For MP3 USB stick issue, it might be a bad connection pin/pins at the end of connectors attached to the headunit which will need you remove all, reinsert them and test.
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