Steps to reproduce:

1. Create new ContentType called "Author" with identifier "author" with "Text line" as a single fieldtype called "name"
2. Create new ContentType called "Book" with identifier "book" with following fieldtypes:
   a) Text line -> "title"
   b) Single relation -> "author" -> mark previously created "Author" CT as a valid relation
   c) Multiple relations -> "authors" -> mark previously created "Author" CT as a valid relation
3. Create new "Author" Content with field name filled as "Joe Joe"
4. Get ID of newly created "Author" Content (in code example content's ID = 58)
5. Using PHP Public API create "Book" content using following code:

           $contentType = $this->contentTypeService->loadContentTypeByIdentifier('book');
           $contentCreateStruct = $this->contentService->newContentCreateStruct($contentType, 'eng-GB');
           $contentCreateStruct->setField('title', 'BOOK PUBLISHED WITH API');
           $contentCreateStruct->setField('author',58);
           $contentCreateStruct->setField('authors',58);
           $draft = $this->contentService->createContent($contentCreateStruct, []);
           $content = $this->contentService->publishVersion($draft->getVersionInfo());

6. Create reverse relation:

        $contentType = $this->contentTypeService->loadContentTypeByIdentifier('book');
        $contentCreateStruct = $this->contentService->newContentCreateStruct($contentType, 'eng-GB');
        $contentCreateStruct->setField('title', 'Harry Potter');
        $contentCreateStruct->setField('author',60);
        $contentCreateStruct->setField('authors',60);
        $locationCreateStruct = new LocationCreateStruct();
        $locationCreateStruct->parentLocationId = 2;
        $locationCreateStruct->sortField = 1;
        $locationCreateStruct->sortOrder = 1;
        $draft = $this->contentService->createContent($contentCreateStruct, [$locationCreateStruct]);
        $content = $this->contentService->publishVersion($draft->getVersionInfo());

7. Try to search for newly created "Book" content by title (exception on v2.5) -> try to access found content (exception on v3.0)
8. Try to access relations tab in "Joe Doe" content (exception on v2.5) -> try to access found content (exception on v3.0)
9. Try to access "Harry Potter" book and check relation tables (v3.0)

Result:
Exceptions are thrown in steps #6 and #7

Expected result:
No exceptions are thrown in steps #6 and #7