When you try to deserialize a protobuf message inside of kafka streams using quarkus, the quarkus class loader has layered loading which causes Class.forName to fail and be blocked. It should be using the current thread class loader.

Currently ProtobufWireFormatDecoder.java at line 72 is
final Class classType = Class.forName(className); But to make it compatible with layered class loaders it should be final Class classType = Thread.currentThread().getContextClassLoader().loadClass(className);