Hi there @VIKASM535239375 

This is mostly due to ACL restrictions, not because of the catalog item or reference itself.

For admin, reference lookups work because admin bypasses ACLs. For end users, the reference field points to a custom table that they don’t have read access to, so the lookup returns no results and dependent auto-population fails.

check these: 

Add a Read ACL on the custom table allowing the intended user roles

check Read ACLs exist for the fields being referenced and auto-populated

If auto-population uses a Client Script + GlideAjax, confirm the Script Include is client-callable and If its client callable it creates a ACL for that script incldude by default. check the roles needed for that.