Ran into connectivity issues again recently. This is the 2nd time in 4 months or so. I have a feeling it's to do with Mac OS' bluetooth not playing nicely with the nrf52 when it sleeps. But since it's such an easy fix and happens so sporadically, I'm not too inclined to investigate further.
Anyway, as promised I just implemented a key-combo to reset bluetooth pairing:
RIGHT SHIFT + LEFT CMD + ESC
The keyboard LEDs should flash three times to indicate all bluetooth pairings have been cleared.
Then just delete the keyboard from your computer's bluetooth and re-pair.