I have tried to reproduce this without your custom model
SELECT * FROM cmis:document as D join cm:titled as T on D.cmisbjectId = T.cmisbjectId where CONTAINS(D, 'PATH:"//."')
This works as expected. The first and third queries will use SOLR; the second the database. I suggest that you configure the search sub-system to always use SOLR and go through the 3 queries again. There are a few things that could explain it.....
Are there any errors? Does the SUMMARY report have any model errors at the end? Do the nodes have the hidden aspect applied?