[5.x]: Craft GraphQL relatedViaField does not narrow entry relations correctly

What happened?

Description

On the remote endpoint https://dev-lawha.plcd.nl/graphql, the entry with ID 214488 exists and direct relation field filters return results. However, when the same relation is queried through relatedToEntries and narrowed with relatedViaField, the response is an empty array. Using relatedViaField at the top level can also trigger a generic GraphQL processing error.

Steps to reproduce

1. Query exhibitions related to entry 214488 with a generic relation filter.
2. Add field narrowing through showItemOfArtist.
3. Compare the result with the direct field filter.

Expected behavior

Only entries related through the requested relation field should be returned.

Actual behavior

An empty array is returned, or the server responds with a generic processing error.

Craft CMS version

Craft Solo 5.9.19

PHP version

No response

Operating system and version

No response

Database type and version

No response

Image driver and version

No response

Installed plugins and versions

No response

Start by reproducing the query against the reported GraphQL endpoint, comparing relatedToEntries with relatedViaField against the direct relation field filter. Trace the relatedToEntries and top-level relatedViaField handling in the GraphQL implementation. Done means the requested field narrowing returns only correctly related entries without a generic processing error.