For OSN3500 devices, when setting the number of fully pinned ports, if the number of ports of the current network element is less than 8, it must be required that the number of fully pinned ports is equal to the number of optical ports, i.e., all optical ports must be fully pinned, or this error will be reported.
Query emslog, found that the network management to 3, 4 boards under the number of fully pinned ports are 1. And query the downloaded network element configuration information found that the 3-N1SLT1 is configured only 1 port, single 4-N1SLT1 is configured with 8 ports, see Annex.

After lab verification, the root cause is finally confirmed:
During the network management download configuration process, after initializing the network element data and adding single boards, for dynamic single boards, all ports will be deleted first. However, the network element does not add all ports by default, for example, N1SLT1 single board 12 dynamic ports, the default sometimes add 12 optical ports, sometimes add 8 optical ports or 4 optical ports. In this example, 8 optical ports are added by default because N1SLT1 is in slots 3 and 4 and the crossover is SXCSA. When the network administrator deletes all the ports, it gets to the ninth port and the network element returns that the port does not exist. When the network administrator sees the deletion error, he does not delete the ports of other dynamic single boards, so he does not delete the ports of the single board in slot 4. The ports of board 4 are still added automatically by the host (8 ports are added by default), which results in an inconsistency in the number of ports for the network administrator and the network element on board 4, which results in an error in the number of ports for the setup of the full overhead.