A homebrewed druid subclass that I'm making is popping up with this message. It makes no sense, though, because all of my features are coded to be granted on the proper levels (i.e., 2nd, 6th, 10th, and 14th). I've tried making the subclass from complete scratch and modifying an existing subclass, but nothing works.

And yes, I have saved the subclass using the main save button. MULTIPLE times. Nothing gets rid of this message to let me share with the community. Sometimes, bugs like this happen with other subclasses and I can just scrap it and do it again (and resolve it like that), but the bug for the druid subclass is insurmountable.

It looks like this issue has been happening since 2018. When will this bug be fixed? Is there a trick to solving this?

I have had that problem several times, but the solutions I use is modify an existing subclass.

You have to be REALLY accurate about getting everything right.

Ughhh that's what I've done already. I've tried from scratch. I've tried modifying. Neither works. It's frustrating. 

For homebrew Druid subclasses, you need a dummy 3rd-level feature.

Sure enough, that worked. Setting one feature to be granted at 3rd level did the trick.