Cannot replace 'Displayed text' of existing links

Thanks for reporting this. I am able to reproduce. Specifically, using a generic installation of the Standard profile, adding Linkit to the Basic HTML text format:

1. Click the "Link" icon.
2. Enter a "Displayed text" value.
3. Enter the first character of an existing node and use Linkit's autocomplete to choose a result from the dropdown. Confirm that the internal path to the node is populated in the "Link URL" field.
4. Quickly(!) Remove the contents from the "Displayed text" input and quickly enter new text and press "Insert."
5. Link text will not be updated and the console will show the Uncaught CKEditorError: Cannot read properties of undefined (reading 'attributes') error.

Additionally, this is something else that doesn't work correctly.
1. Click the "Link" icon.
2. Enter a "Displayed text" value.
3. Enter the first character of an existing node and use Linkit's autocomplete to choose a result from the dropdown. Confirm that the internal path to the node is populated in the "Link URL" field.
4. Now click "Link URL" field again and enter the first character of another node and use Linkit's autocomplete to choose a different result.
5. The link field will NOT correctly populate the internal path to the node but will simply populate the character you entered.

I've merged a number of changes related to CKEditor v45 compatibility to reduce the surface area here. The originally reported problem still remains, so this is "Needs work."