Phantom subclass (And Arcane Archer for Fighter) unavailable despite WoTC claiming "As the new classes are backwards compatible - we’ve ensured that all the previous subclasses from books published by Wizards of the Coast work without any issues for the 2024 classes." 

Noticed this as well.  Strange, where is Phantom?

I've noticed all the third party subclasses missing, too

This is a serious oversight, they outright claimed ALL WOTC published books had their subclasses made backwards compatible, but here Phantom Rogue sits again, first WOTC completely screwed the pooch on the mechanical design by only allowing it to be viably online at level 9 with a feature that could easily be given at level 3, and then they've completely forgotten it exists for D&Dbeyond?

I noticed this as well, despite having Tasha’s cauldron available to me, it doesn’t show up. I made sure legacy was turned on just in case, but nope. Still not there. 

I have nothing constructive to add. Just upset that my main characters subclass happened to be one of the few to get screwed here.

Same, making 2024 versions of my player's characters so they can decide which to use, and can't finish 2 of them because of this.

Have they acknowledged any of these issues? My playgroup is struggling due to the same.

Still sitting waiting a week after my "early access" without the content I need to update my character. How exciting.

Quote from Dasler >>

Have they acknowledged any of these issues? My playgroup is struggling due to the same.

 Not yet, I doubt they see it as a priority.

i have a ticket open currently to see what the deal is

Quote from Svenjam1n >>

i have a ticket open currently to see what the deal is

 Any update?

Same!  Just went to build a Rogue and despite owning almost all the rule sourcebooks there are only a few options listed there for subclass