Have you checked the image version of the Edisons? Run the following command in both Edisons to check the version: configure_edison --version
From your description, the image version might be the cause of the issue. If so, re-flashing the modules might fix it.
I am using a custom image built from SDK release 2.1. I have removed the oobe package, so configure_edison is not available.
What modules are you talking about reflashing?
I am using the mcu_fw_loader systemd service to load my MCU image from /lib/firmware/intel_mcu.bin
Thanks, I realized that my upgrade process has been updating the boot and rootfs partitions, but was not upgrading the mmcblk0boot0 and mmcblk0boot1 partitions, so the low level firmware used for the system and MCU was not getting updated. After upgrading those partitions, the MCU now works on several of the Edisons that I tested.