OK. So we've established this problem has affected the following models:
MacBookAir8,1 (MacBook Air (Retina, 13-inch, 2018))
MacBookPro11,2 (MacBook Pro (Retina, 15-inch, Mid 2014))
MacBookPro13,1 (MacBook Pro (13-inch, 2016))
MacBookPro13,2 (MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports))
MacBookPro13,3 (MacBook Pro (15-inch, 2016))
If you're seeing the same issue and your Mac isn't listed above, please post your Mac details so we can add to this list.
More interesting, if you're Mac is listed above but you are not having this problem, can you confirm that too, please?
FYI: My own Mac does not have the issue and yet is on the above list (MacBookPro13,3 (MacBook Pro (15-inch, 2016)))
Perhaps eventually we can provide Apple with enough information to figure this out. I'm still thinking it's firmware related.
My Mac's firmware (for the MacBookPro13,3 (MacBook Pro (15-inch, 2016)) is 429.60.3.0.0 - does anyone have a different version of firmware for this Mac?