Your increase is on RECEIVE - "Long frames" - that translates to: "Number of received frames that were greater than the maximum size and had a valid CRC."
That suggest you either have large MTU set somewhere on the LAN but not on the broadcast domain this interface assigned to in ONTAP.
Another option i may think of is if your switch configured to trunk with a native vlan (and that's works ok, and it's a common configuration), but it also has VLANS allowed on - that are not configured in ONTAP .So when the switch also send some vlan tagged traffic that adds up to your frame size. (regardless if the traffic even meant to the filer or was just a broadcast).
if you want to see the traffic in your own eyes, you can collect a pktt.
We have the same issue with a brand new FAS8200/AFF 300 MetroCluster.
We got the following message every hour from every node (from every ethernet port):
vifmgr.cluscheck.crcerrors: Port e0h on node xxxxx is reporting a high number of observed hardware errors, possibly CRC errors.
This message occurs when a network device reports a high number of observed hardware errors, such as CRC errors, length errors, alignment errors, or dropped frames.
The errors could be originating from the specified port, a remote port, or a port on another component of the network. Check the statistics for both the port and the switch. Contact NetApp technical support for assistance and specific instructions.
we observer the same errors on our 10Gbit/s ports with MTU size 1500 (Netapp FAS2620), and we have open (for months now) a case to try identifying the cause of those Warning Messages, but no success with Netapp and the Network tcpdump we send them.
Netapp FAS are connected to HPE Switchs, ports on switch side are Jumbo frame enabled, we try to modify the frame size to the min allowed on HPE Switch (1536), but messages persists (at almost fixed time every day with a 10 min delta day after day).
Did you have open a case to Netapp Support? Have they confirm a KB or Known issue related to those messages?
We just upgraded last week from 9.2P4 to 9.3P10 and are now experiencing the same issue, on the same port actually (e0h). It's only one node out of our four node cluster. We are also getting alerts on e0b indiciating "Excessive link errors on network interface e0b. Might indicate a bad cable, switch port, or NIC, or that a cable connector is not fully inserted in a socket. On a 10/100 port, might indicate a duplex mismatch."
I believe both are false positives as we were getting 0 alerts on either interface before the upgrade. Will be opening a case today.