My MX Mechanical keyboard is paired with my iMAC as #1 and my PC as #2. I've always used it with my PC. But oftentimes, when I wake up my PC, the keyboard would still connect to my PC (#2), but after a few key strokes of inputting password, it would switch to #1 by itself and wake up my iMac, and remain connected to iMac instead of PC.

My other logitech keyboards (MX key, K370/375,etc.) with the same pairings never have this problem.