i have the 65mm spindle and up until a couple days ago when i powered down the spindle it just stayed put, now it drops until it hits something, ive had the machine a few months so this is a new feature ,
its also a lot hotter than its been so don’t know if that has something to do with it or just parts loosing up.
I also just got done machining a lot of aluminum parts so its been having a workout to say the least
i see that Carbide offers a strut kit just for this issue,
just seems weird
There is something of a balancing point here, and some folks manage quite well w/ the stock setup (no gas strut), while other folk’s machines drop almost instantly and there is a definite need to address this — one theory I’ve had is it’s the weight/run of the vacuum hose which makes a difference — even if the machine drops, some folks just put a block of foam under the Z-axis before shutting down.
The Z axis generally has really low friction, which in and of itself is a good thing. But that does mean gravity can do it’s job better. 
On the SPro at work, the Z axis stays up. On my S5Pro, the Z axis dropped… with both having the 65mm spindle. I just had a prop rod I put under before shutting down.
[Friday comment] I need to read the thread titles a little more carefully. At first glance I saw “Spindle drops off when powered”…
Mine has dropped pretty much from day one. You’re not alone. But also, it hasn’t made a difference in anything.