Suddenly unable to add an approver - no options showing

[Deenie Petros]

We have a service management ticketing JIRA board which has been in use for a few years.  The flow for the ticket types has not changed, neither has any permissions on the board.  I am an admin on the board.  Once we set the status to 'awaiting approval' it prompts to 'add an approver'.  Starting yesterday, no one is able to add an approver.  We click the button and start searching and get 'no options'.   There is no list, and we have no way to enter either a name or email in the field.  I've tried a few suggestions searching here for solutions but none of them have worked.  Any ideas on what could have happened or how to correct this?  Thank you. 

[Jameel Ahmad]

JIRA service should use for ticketing and allowed permission on the board you set the status and approve to get option.

[Deenie Petros]

Its been set up that way and working for 2 years... no config changes on the board.  Suddenly the search for adding the approver yields no results.