Bluetooth module intermittently drop connection to all connected bluetooth devices (Magic Mouse/Keyboard, Speakers, etc.)

Systems:

iMac 27" Late 2013

macOS Mojave Version 10.14.5

Symptoms:

Bluetooth module intermittently drop connection to all connected bluetooth devices (Magic Mouse/Keyboard, Speakers, Sony Headphones, etc.). It will drop for 1~3 seconds and will then auto-reconnect. This problem happened after updating to Mojave Version 10.14.5. This is not a bluetooth devices issues, because all connected devices got disconnected at the same time.

Tried the following Bluetooth "Debug" section - holding [Shift]+[Option]+click on Bluetooth:

(1) Reset "Reset Bluetooth Module"

(2) Factory reset all connected Apple devices"

(3) "Remove all devices"

Results: Does not help.

Tried resetting SMC, PRAM, NVRAM

Results: Does not help.

Tried deleting apple.Bluetooth.xxx files

Results: Does not help.

Tried unplug all other USB devices

Results: Does not help