So about some of the new things.

Question can you see an issue? 

https://www.dndbeyond.com/characters/173298565

Take your time, no homebrew, 100% DnDB purchased conent, plus drops. 

Spoiler: 

so to make this point clear as day. 

https://www.dndbeyond.com/characters/173300607

also in order to use a subclass feature, I had to add from Homebrew on this because someone at DnDB forgot to add Vestige Campanions to familar creatures. woot. /facepalm

Something similar has been possible ever since the release of the 5.5e core books, as it'll let you add both 5e and 5.5e versions of the same class to the same character if you turn off multiclass prerequisites. I doubt they're going to do anything about either issue; the whole point of allowing you to turn off the multiclass prerequisites is to let you do weird stuff that's outside the normal rules.

The Vestige doesn't show up in the Extras tab because it has dynamic stats. It's not that they "forgot", it's that the Extras tab doesn't support creatures that have stats that depend on the stats of their owner. It's similarly an issue with Beast Master Rangers, Battle Smith Artificers, and a whole bunch of summoning spells.

Quote from wagnarokkr >>

Something similar has been possible ever since the release of the 5.5e core books, as it'll let you add both 5e and 5.5e versions of the same class to the same character if you turn off multiclass prerequisites. I doubt they're going to do anything about either issue; the whole point of allowing you to turn off the multiclass prerequisites is to let you do weird stuff that's outside the normal rules.

While yes, with 5.0 and 5.5 that is clearly a break in design, the fact that they treated WOW  as a new edition like that will cause this to be an issue, as no where in the WOW rules book does it say you can not multiclass, yet to multiclass at all you have to disable that function. Which opens it up to multiclassing with the same class. 

As a forever DM, who runs games in my own settings, and who uses all books and multiclassing, this means if someone wants to start with a Void Elf warlock they can in my games, and if they want to multiclass it's allowed at my table. The flaw that DnDB did is not to add a  new builder tab for WOW which was basically a prebuild character, and just to include the WOW options in the normal way. This way a new WOW player gets a prebuild with optional WOW race as pre designed classes, and experienced D&D players can just use material as normal.