We used to be able to plant the egg seed to get an egg plant but now I get this error message: That seed type does not exist! Is this a glitch or was it changed?

As far as I know it wasn't changed. Many seeds are glitched, it seems to happen any time new seeds are added to the garden - some of the new seeds end up glitched, and some of the old ones also do. Report it in the bug forum.

Thank you! Submitted.