API response for IRIs at search and select endpoint provide "random" results

[rombaum]

Describe the bug
In OLS3 the select and search APIs provides the possibility to search for an IRI and the first results is an exact match for the requested IRI if the IRI is indexed by OLS. In OLS4 totally misleading 'random' responses where shown. In order not to make the problem unnecessarily complex, I will only focus on the Select API. Nevertheless the select and search APIs are affected from this behavior.

To Reproduce
Steps to reproduce the behavior:

1. Go to the select API with the value http://purl.obolibrary.org/obo/NCIT_C2985
2. Have a look to the first result of the response.
3. See misleading 'random' first result and not the exact Match for NCIT:C2985

Expected behavior
The first result should match the requested IRI since it is an exact match and indexed to OLS4.

Screenshots
If applicable, add screenshots to help explain your problem.

Response of the select API of OLS4 for NCIT:C2985 with the first results

Response of the select API of an OLS3 system (SemLookP) for NCIT:C2985 with the first results

Response of the select API of an OLS3 system (TIB TS) for NCIT:C2985 with the first results

Additional context
Some application only save the IRI of a concept in their local database. With this IRI additional information such as ontology, label, synonym, description are requested by a call from the OLS API. To ensure the backward compatibility the original behavior should be provided again. I would guess that the index process must be changed or corrected. Since, I also found out that the results for string are misleading as well. I will create another issue #860 for this.

f.y.i. screenshots for the search API:

Response of the search API of OLS4 for NCIT:C2985 with the first results

Response of the search API of an OLS3 system (SemLookP) for NCIT:C2985 with the first results