When the router has several synchronization sources (PTP/SynchE) across different line cards, the unexpected active synch source switchover can happen.

After a change in some parameters in PTP Announce message from the upstream PTP peer the router can switchover to the new synchronization source and very shortly back again to the previous synchronization source. For example, the following logs identify the interface change from slave (so the interface is used to receive the synchronization from the grand master) to master (so the interface is used to provide the synchronization to the downstream devices) and after 2 seconds - back again.

Dec 22 13:47:20.050 2022  ti0014a400-re0 : %PFE-6: fpc10 PTP-LOG: ptp_update_stateful_port_state STATEFUL: Port 0 (ae1.0) Change to SLAVE
Dec 22 13:47:20.068 2022  ti0014a400-re0 : %PFE-6: fpc2 PTP-LOG: ptp_update_stateful_port_state STATEFUL: Port 0 (ae0.0) Change to MASTER

Dec 22 13:47:22.064 2022  ti0014a400-re0 : %PFE-6: fpc2 PTP-LOG: ptp_update_stateful_port_state STATEFUL: Port 0 (ae0.0) Change to SLAVE
Dec 22 13:47:22.111 2022  ti0014a400-re0 : %PFE-6: fpc10 PTP-LOG: ptp_update_stateful_port_state STATEFUL: Port 0 (ae1.0) Change to MASTER

The parameters in PTP Announce message from the current synchronization source can become even better: like PTP  CC (clock class) changes from 33 to 32) - but still the 
switchover from this synchronization source can happen.

No service impact was reported after such switchover but theoretically if the new synchronization source provides relatively different synchronization sygnal, the service can be impacted (e.g. interface flap).

The fixed releases can be seen in the PR1803105.