Magic Keyboard and Mouse disconnecting after sleep.

Since the last update to 10.14.5 after my iMac wakes, the mouse and keyboard both disconnect and reconnect over the next 10 seconds.

I have;

Deleted (from User, Library, Preferences), bluetooth.plist (several times throughout troubleshooting process).

Through the BT debug option...

Factory Reset Apple Bluetooth devices

Reset the Bluetooth module

Removed and re-added all devices.

Reset the P-RAM (Power down, Boot - CMD, OPT P & R) and also SMC (power off, disconnect cable and depress power button).

I thought this last one had done it, alas, it's started again today.

Anyone else suffering the same and moreover, found a solution?

Any help obviously gratefully received.