Resolved 10.14.6 BT 4.0 Dongles problem fixed

[MIKX]

I use a Japanese Elcom Bluetooth 4.0 USB dongle in my 2009 4,1>5,1 Mac Pro - it has worked well in High Sierra and up to Mojave 10.14.5. with phenomenal range. ( I live in Japan ).

Apple made some BT changes in Mojave10.14.6​

1. My USB BT verson 4.0's Dongle's range was dramatically reduced

2. It seems that in fact the Internal BT module was connected . . my USB BT 4.0 dongle
WASN'T connected. I also found that none of my five BT Version 2 dongles were
recognised.

Solution​

1. I disconnected my internal BT Module's cable. ( behind the CPU tray ).
( Shut down, remove power cable and remove the CPU tray. the BT module is behind
where the CPU tray was .. on the right side of the backplane.
Just ( gently ) slide the module's cable to the left to disconnect it.)

2. I deleted ( Mojave 10.14.6 ) Library/Preferences/com.apple.Bluetooth.plist

3. I copied " High Sierra 10.13.6 / library/Preferences/com.apple.Bluetooth.plist "
to the same to the same location in Mojave 10.14.6

4. Shutdown - cold startup

5. Ran an iTunes big playlist - paired my Bluetooth headset

6. Voila ! Original range is restored - I can now walk anywhere around my home
without any BT disconnection.

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I have a total of 14 USB 2.0 slots available to me plus 4 USB 3.0 on a PCI card.
My BT 4.0 dongle is located in one of the cMP's front two USB 2.0 ports = increases the range a little.
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OFF TOPIC NOTE :
A simple solution to random BT headphone / headset disconnection is to run a large iTunes playlist with AUDIO VOLUME SET TO ZERO.
iTunes will complain with a popup. . just hit the " Don't popup again " button.