Time Machine "There are no disks to back up." Cannot remove MHD from excluded list.

I just noticed the same thing. My last backup was at 9:55 AM today, just before I installed Beta 2 update 1.

When I look at the list of backup destinations (I have 3) each has a red "i" that provides says that Time Machine couldn't complete the backup because there were no disks to back up. Looking at Options reveals that my Macintosh HD has been added to the list of exclusions.

Like benpeke, I can't unselect the hard drive.

This seems like a serious bug in update 1.

Same thing here. I've filed rdar://33069385 with a sysdiagnose and tmdiagnose

Ok, I really should read the release notes more carefully:

As noted in the Release Notes, this is the intended behavior if your system partition is formatted with APFS.

Due to a known bug in the feature for local snapshots, Time Machine is intentionally deactivated for the root volume.

I'm also having this issue.

I didn't see release notes for update 1 as it was installed via software update. Is this in the release notes for beta 2?

Having the same issue myself.

It's in the release notes for beta 2 update 1. Yes, they released an update to beta 2 almost immediately after they released beta 2.