Valid Query for mixin Type in JCR 2.x fails in Oak

In a Sling based environment running on Oak 0.12.0.r1548152b I'm facing an issue resulting in a 500 error in Sling due to a repository exception when executing the following query through the Sling Resource Resolve
that did work in the equivalent JCR 2 based environment.

resolver.findResources("SELECT * FROM [my:custommixin]", Query.JCR_SQL2)

The custom mixing was added to the reqo via vlt package (mvn-vlt plugin by Adobe) and results (as well as the corresponding XPATH version in the following stackstrace:

javax.jcr.RepositoryException: Query contains more than one selector: []
	at org.apache.jackrabbit.oak.jcr.query.QueryResultImpl.getNodes(QueryResultImpl.java:163)
	at org.apache.sling.jcr.resource.internal.helper.jcr.JcrResourceProvider.findResources(JcrResourceProvider.java:261)

The further stacktrace seems irrelevant, but I can provide more if required.