For my player who is a level 5 Druid using a homebrew subclass both of us can't add cantrips beyond 2. We can take away or add spells level 1 or higher, but the website crashes when we add cantrips.

New Development:

It only crashes now when adding the Thorn Whip cantrip.

The Thorn Whip cantrip is, I believe, the only Druid cantrip not in the Basic Rules (ie, not free). Do either of you own the PHB on this site, or have purchased just the spell(s)?

There is a recent issue where a DM editing a player's character sheet will see the spells the DM owns, whether or not they are shared with the campaign. Attempting to add the spell causes the error you noted.

If you have Content Sharing enabled for the campaign, then turn it off and back on again, and then reload the character sheet page, and see if that fixes the issue.

And if you don't have content sharing, the intended behavior is to not be able to add Thorn Whip (although it's not supposed to crash).

The best solution if you lack Content Sharing is to make a homebrew copy of the spell (don't publish it). That should be useable without issue.

This is intended site behavior.

By default, a player should only have access to content that they have purchased or is free (Basic Rules).
Content sharing with a master subscription means that the player has access to any content that anyone in the campaign owns, for characters in that campaign only.

Allowing DM edits to select spells for PCs in games without content sharing enabled was a bug, not a feature, as it bypassed the content sharing restriction.

Oh ok I understand now thank you for helping!