Rexaar

You must have unequipped your secondary weapon, it is required for some class to attack.
You can buy another one from a npc named "Neville" in most towns if you can't find it in your inventory.

You still need to do the pet snack quest to have multiple pet. I have not heard anything about it being broken the past few months.

There has been people saying their maple reward shop has some stuff restocked and some stuff go missing after the patch.
My stock of black cube went missing, and my fury totem stock went up, and my monster park ticket stock went down too.

Comparing the kms mastery level, the total SP needed for xenon is still the same and they keep their wiki well updated so the same mastery level mean nothing changed.

https://namu.wiki/w/%EC%A0%9C%EB%85%BC(%EB%A9%94%EC%9D%B4%ED%94%8C%EC%8A%A4%ED%86%A0%EB%A6%AC)/%EC%8A%A4%ED%82%AC

https://namu.wiki/w/%EB%A3%A8%EB%AF%B8%EB%84%88%EC%8A%A4(%EB%A9%94%EC%9D%B4%ED%94%8C%EC%8A%A4%ED%86%A0%EB%A6%AC)/%EC%8A%A4%ED%82%AC

In short, KMS patch note lied (it on their official site patch note too), or was not specific on who got their mastery level changed

It is intended for Xenon to not have enough SP to max out all skills in 2nd/3rd job.
It is intended for Luminous to not have enough SP to max out all skills in 1st/2nd/3rd job.