When you declare a type in a DRL using the "declare" syntax, that type cannot be referenced by Drools LHS expressions in a Sequence Flow (for example in the context of an X-OR Gateway). The DRL and BPMN2 file are in the same project.
The problem is the order of compilation of CompositeKnowledgeBuilderImpl. The builder compiles the process definitions before the DRLs, which results in a situation where the declared types used in the process are not yet available in the Drools ProjectClassloader when. the process is compiled.
Easy fix is to compile the process after the rules, which makes sense as the rules will normally not really on processes, but processes can really on rules.