Switch with &&& and ||

I think this might just be an order of operations issue I think that the logical AND is evaluated first, then the OR.

So effectively you have:  condition1 || ( condition2 && condition3) || condition4 

Whereas I think you want: (condition1 || condition2 ) && (condition3 || condition4)

I think adding extra brackets to force the order of operation you want might fix this:

CY Activity = SWITCH(
TRUE(),
([1. Jan v2] = 3 || [1. Jan v2] = 5 ) &&
([1. Feb v2] = 3 || [1. Feb v2] = 5 ) , 1,
0)

 I often use extra bracket if I have multiple logical AND/OR combinations to clarify the ordering