Earlier today this started to flap in asw2-d-eqiad logs:
May 14 16:15:28 asw2-d-eqiad fpc1 Rear QSFP+ PIC Chan# 3: Rx loss set
May 14 16:16:28 asw2-d-eqiad fpc1 Rear QSFP+ PIC Chan# 3: Rx loss cleared
Unfortunately, the logs are not clear on which port is having an issue.
asw2-d-eqiad> show chassis pic fpc-slot 1 pic-slot 1 [...] Fiber Xcvr vendor Wave- Xcvr Port Cable type type Xcvr vendor part number length Firmware 0 40GBASE CU 3M n/a FiberStore QSFP-40G-DAC n/a 0.0 1 40GBASE CU 3M n/a FiberStore QSFP-40G-DAC n/a 0.0 2 40GBASE CU 3M n/a @i```Bdl \x10\x10 n/a 0.0
asw2-d-eqiad> show chassis hardware [...] Xcvr 2 REV 01 74 A QSFP+-40G-CU3M
It looks like the 3M DAC connected on fpc1:1/2 to fpc2:0/48 is faulty.