Today I have two small updates and two good news at the same time. I fixed Ethernet on my v0.1.1 board and just finished configuring PXE with this board. At the moment I am finalizing tutorial on how to netboot CM4 connected to uCM4, as it turned out to be less obvious than I thought.
Getting back to Ethernet issues, this indeed turned out to be soldering problem. After reflowing both connectors, problems disappeared. Fun fact is that I was forced to do that, because I destroyed high speed connector few days ago, when disconnecting CM4. It turned out to be soldered so badly that I broke it, instead of disconnecting. Anyway, this forced me to fix the thing and in the meantime I checked that Hirose connectors could still be fixed, when pins fall off the connector chassis. And finally I learned how to solder them quickly and successfully, so if you are interested in getting some advice, let me know and I can consider describing it from newbie perspective (it seems that I am still lacking experience in soldering).
Expect tutorial in coming days!