I finally gave up trying to make sense of the connectivity. I scavaged a router, set the address to 10.10.10.1, setup the dhcp pool for 10.10.10.0/24. Reconfigured the mac mini ethernet adapter and the DSJ to use DHCP.
Everything reconnected like it did with the crossover cable and the ethernet 10/100 switch experiment.
Play back through the bridge is not dropping out any more for 44.1 or DSD64 using Roon. audirvana on a mac book pro was able to play through the bridge as well.
So for whatever reason, a router and DHCP appear to have made a difference in bridge play back. Go figure. The network is still isolated as it was with the switch or crossover cable implementations.
Thanks for the comments and taking the time.