When ECMM[0], it means that the MM board is in normal state. When ECMM[1], it means that the MM board may have problems, or it may have poor contact with the hash board.
You need to check the MM board first. Also, as BitMaxz said, check your third hash board. If you want to find faulty chips quickly and accurately, you'd better have an Avalon hash board tester. If you don't have the enough budget, you can buy a tester without a screen.

Hashboard shows 0 chips usually due to abnormal power supply or chip short circuit. Others will have more helpful suggestions if you can provide kernel logs. .

Yes, chain 2 refers to the third hashboard. For temp sensor issues, you can check this thread: https://bitcointalk.org/index.php?topic=5244120.0