Got Z9 back from Nikon, and they Effed up the Focus

Now the Z9, hunts back and forth for focus. If something was in Focus, and I repress the Shutter or Back Focus Button, major defocus occurs before returning to focus. It didn't do this before, and I had saved my settings prior to sending it in, and reinstalled them. Does this with all my Lenses, so it will be going back again. I wonder what they will Eff up next?
They did upgrade the FW to 4.01, I wonder if that caused this. Every new FW so far has seemed to degrade the Performance of the AF.

Post a pic of the Z9 with the lens you are using.

My goodness, how unlucky you are. First a D850 that did not work properly and now your Z9 is a disaster.

I have owned lots of Nikon gear that has always worked perfectly. I have 2 D850 bodies and 2 Z7 bodies that are faultless. Some people really are unlucky, every camera they buy is a dud. Or is it the owner that is a dud?

Or the owner possibly was never in possession of any of them.

I own the Z9 and used to own the d850. Happiest Day of my Ownership of the D850 was the Day I got rid of it. I still have my D200, it certainly worked better than the D850 I had. In between I had the D7000, D800, and D810.

I offer my own experience:
Bought the Sigma 150-600C the first one was damaged in transit and returned, and the second one is perfect.

I ORDERED Sept 14th the 180-600Z - and the delivery for the 18th was canceled 8 hours before - On the 17 night an accounting bug resulted in me not paying Amazon orders for 15 months. Automatically my account was blocked, my orders and my deliveries were cancelled - 48 hours of pain while they solved the issue.

Re- ORDERED Sept 19th - Delivered on the 23rd, a Nikon box damaged inside a big Amazon box. The lens was freely running around, damaged

Re-Re- ORDERED Sept 24th - Delivered Oct 7th, Nikon box delivered naked, a corner crushed - the lens is only slightly soft 😢

That doesn't stop all my life ... I refurbished my kitchen:

• Induction range, I ordered 5 before getting the right model AND a working copy
• The Owen, it was completely reimbursed by Amazon and I kept it. The seller sent the wrong model and never answered the request to change it. With that money, I called the Samsung service and replaced the parts.
• The fridge, it was okay!! After three days cracks appeared in the internal food containers - Samsung replaced them

The gift TV for Mother's Day:
6 orders. One was finally the right model but with a HOLE into the screen - there was a 3mm hole in the corresponding position in the box right on the "i" dot of an inscription, invisible to a box control.

Sometimes I'm worried: I buy something new and it works perfectly!
It will stop usually before the end of the guarantee:
like the three toasters in a row in 180 months - Amazon replaced no issue.

My two TVs as well:
the Samsung 55" got the motherboard replaced....
.... and the same guys came back 7 days later to change the screen of my brand new Samsung 65".
An insect made a home inside the LED sandwich it took me three days to discover it was not surface dirt.

( they have a long story in the notes on my account both in Samsung and Amazon )