One note on the DM3 and JCT products. The DM3/JCT boards were sold to Sangoma Technologies on January 9, 2018. While the API interfaces are similar between DM3, JCT and HMP products, the underlying internal architecture does differ and event timing may be different based on the architectures. If there are questions between JCT and DM3 board event processing, it may be best to touch base with Sangoma directly.
All that said, the programming choices, buffer sizes, ... etc, that Jeff alluded to may also come into play.