Bought a new Profitec Pro 600 and when I pull a shot around 15-20 seconds into the shot the pressure gauge drops a little bit, from around 8.5 bars to around 8 bars. Is this normal? Or could there be something faulty with the machine. I think my puck prep is decent. I WDT, level, and use Force Tamper.

Also, potentially related or unrelated, my machine has a flow control valve on it and the pressure gauge reading at the brew group. When pulling a shot the pressure reading at the brew group is always about .5 a bar higher than the pressure reading from my machine. Is this normal? I'm under the impression that if I set my pressure on my machine for a max output of 8.5 bars, the pressure at the group can't possibly be higher correct?

The puck degrades and offers less resistance during the shot. You're not seeing anything odd or strange.

Here's a post with some pressure profiles I recorded on my Bianca:
viewtopic.php?p=815734#p815734

Thank you Bruce, really appreciate the insight as I am new to brewing espresso.

Any idea on the brew pressure readings I'm getting? Is it normal for pressure reading at the group head to be higher than my set pressure from the pump? Or is something potentially faulty there.

I'm not sure of the full mechanics, but I have seen some brew pressures exceed the pump pressure. My pump pressure is ~10.25 bar, which also matches the what I see when using the blind basket to back flush. I've seen 11 bar with a wide open paddle and a choked shot, but I almost never run my machine with the paddle wide open anymore. I'll probably get around to reducing my pump pressure eventually, since it isn't difficult to change, but it's easy enough to keep the brew pressure at a reasonable point with the paddle.

You're good. I have my OPV set to 8.5 bar on my PRO600. If the shot never reaches that its an indication I can tighten my grind but shots always lose pressure and speed up in flow as they run.