Performance + Search Mode is a feature which gives you ability to use Performance search with extra security layer.
Only users which have View Field Permission will be able to search the Secure Field values.
The mode can be configured for each Secure Field separately.
To enable the mode certain condition must be satisfied:
Custom field must be in Performance Search Mode.
Only one field context can be applied to the Secure Field.
View Field Permission for the field must contain only Single User Or Group.
Enable Performance + Search Mode
Adjust View Field permission:
Log in as a user with the 'Jira Administrators' global permission.
Navigate to Admin menu → Issues → Custom fields permission schemes. Locate needed scheme and click Permissions.
Add Single User or Group option for View Field permission.
Visit Custom field configuration
Edit Performance + Search Configuration