Request Field Value Changed to Wrong Value

I entered the below value into a request field on the Simple 301 Redirects screen:
/%year%/%monthnum%/%day%/%postname%/

After clicking the Save button, that value is transformed into:
/%year%/%monthnum%/y%/%postname%/

Notice that in the above string, the “da” characters have been removed from “day”. This breaks the redirect.

My goal is to update my permalink structure and add redirects as shown in the “Using the Simple 301 Redirects Plugin” here:
https://www.wpexplorer.com/change-permalinks-wordpress/