If no collection table is specifically mapped and an entity name is specified (via @Entity(name="...") , the table name generated for @ElementCollection starts with its (unqualified) owning entity class name. It should start with the mapped entity name instead.
Currently, the collection table is named "Matrix_mvalues"; it should be "Mtx_mvalues".
Fixed in 4.3.6 and 4.2.15. It will be fixed in master by HHH-9281.
Closing resolved issued in preparation for releasing 4.3.6.