Cannot add Plan Description after adding a new Access Plan

### Reproduction Steps

1. Install and activate the Classic Editor plugin
2. Edit a course
3. Under Access Plans, click Add New
4. Try to enter a Plan Description

### Expected Behavior

You are able to enter a plan description

### Actual Behavior

You cannot enter a plan description

### Workaround

Click Save first (plan description isn't required), then you are able to enter a plan description.

This issue has be recreated:
+ [ ] Locally
+ [ ] On a staging site
+ [ ] On a production website
+ [ ] With only LifterLMS and a default theme