We had this as well. We specifically blocked TVOS 18 and they all updated. We have been working with JAMF and Apple on a related issue where Apple TV 4th Gen is not letting iOS or iPadOS 17.5.x users screen mirror for more than 5 minutes at a time.

same issue here! 

Interesting. Did this issue happen prior to updating to tvOS 18? Or did it happen after doing an putting your iOS and iPadOS devices on 17.5? I’m just curious!

Our defer for iOS and iPadOS are both working but somehow tvOS decided to update. Super strange...

Thank you so much for the information.

I opened a ticket with Jamf. The case has been escalated to the developers. apparently it is not a problem with mdm because everything seems to be correct in the defer payload. They are trying to escalate the problem to apple and find out with them what the cause is.

We had the same problem with our Apple TVs; they all updated automatically to tvOS 18.0, along with all the related issues.

Are your Apple TVs also configured in conference mode?

I suspect that devices configured in conference mode are updating automatically. Our devices are still updating themselves; they're currently all on tvOS 18.6 without us sending an update command.

The Software deferral  profile doesn't seem to work at all.

I have a feeling the devices will update automatically to tvOS 26 as soon as it's released.