If you had a newline token in your custom prompt ($nl), you'll need to set your custom prompt again manually and replace $nl with @nl if you want it to work.

CONFIG PROMPT CUSTOM by itself will show you the raw version of your prompt with all its tokens, so you can easily just copy it back in with the edits.

Penned by my hand on Tisday, the 13th of Niuran, in the year 463 MA.