I have a similar issue using 200G-LC board with 10.6.2 version. When I configure a new circuit, from time to time I have a Sync Loss alarm. For clearing the issue, I have many options, but none is 100% reliable : - delete and recreate the PPM port -c...

I still have a similiar issue in 10.6.2 with 200G-LC board. The client is a Cisco router with QSFP28 SR4 (ncs5k16, ncs55A2, ncs55A1, nexus 7706).   When I configure a new circuit with CPAK SR4,  from time to time, I have a SYNCLOSS in the client port...