Unable to select the next activity

Summary:

I want the technician to select the next activity from the dropdown on activity completion

Content (please ensure you mask any confidential information):

I have enabled the option of "Allow selection of the next activity on Complete" when completing an activity and, while I cannot select the next activity (it shows greyed out) on completion screen.

I would like the technician to be able to manually select the activity

Version (include the version you are using, if applicable):

24B

Code Snippet (add any code snippets that support your topic, if applicable):