Internal NIC being reported as down periodically

Periodically I get bursts of kernel messages related to internet connected NIC going down. What might cause this? UTM is connected to ISP modem that's in router mode for what that's worth.

It's a 3 wk old unit where there was only ISP router before. There aren't widespread reports of connections failing, maybe because it's only for a couple seconds and people are blaming the other end. There was a complaint of zoom session reporting bandwidth was low (which never happened before UTM) but think that was fixed by excluding zoom.com from web filtering (not yet confirmed).

Any info would be appreciated.

2021:03:07-12:19:28 lyneutm kernel: [316673.226072] igb 0000:02:00.0 eth1: igb: eth1 NIC Link is Down
2021:03:07-12:19:28 lyneutm kernel: [316673.226134] br0: port 1(eth1) entered disabled state
2021:03:07-12:19:31 lyneutm kernel: [316676.529641] igb 0000:02:00.0 eth1: igb: eth1 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX/TX
2021:03:07-12:19:31 lyneutm kernel: [316676.529783] br0: port 1(eth1) entered forwarding state
2021:03:07-12:19:31 lyneutm kernel: [316676.529801] br0: port 1(eth1) entered forwarding state
2021:03:07-12:19:46 lyneutm kernel: [316691.548052] br0: port 1(eth1) entered forwarding state
--------

2021:03:07-12:29:00 lyneutm kernel: [317245.206282] igb 0000:01:00.0 eth0: igb: eth0 NIC Link is Down
2021:03:07-12:29:00 lyneutm kernel: [317245.206345] br0: port 3(eth0) entered disabled state
2021:03:07-12:29:02 lyneutm kernel: [317247.414163] igb 0000:01:00.0 eth0: igb: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX/TX
2021:03:07-12:29:02 lyneutm kernel: [317247.414302] br0: port 3(eth0) entered forwarding state
2021:03:07-12:29:02 lyneutm kernel: [317247.414321] br0: port 3(eth0) entered forwarding state
2021:03:07-12:29:17 lyneutm kernel: [317262.440610] br0: port 3(eth0) entered forwarding state
---------
2021:03:07-12:30:32 lyneutm kernel: [317337.009373] igb 0000:02:00.0 eth1: igb: eth1 NIC Link is Down
2021:03:07-12:30:32 lyneutm kernel: [317337.009432] br0: port 1(eth1) entered disabled state
2021:03:07-12:30:33 lyneutm kernel: [317338.717503] igb 0000:02:00.0 eth1: igb: eth1 NIC Link is Up 10 Mbps Full Duplex, Flow Control: RX/TX
2021:03:07-12:30:33 lyneutm kernel: [317338.717646] br0: port 1(eth1) entered forwarding state
2021:03:07-12:30:33 lyneutm kernel: [317338.717665] br0: port 1(eth1) entered forwarding state
2021:03:07-12:30:34 lyneutm kernel: [317339.376656] igb 0000:02:00.0 eth1: igb: eth1 NIC Link is Down
2021:03:07-12:30:34 lyneutm kernel: [317339.716391] br0: port 1(eth1) entered disabled state
2021:03:07-12:30:37 lyneutm kernel: [317342.268387] igb 0000:02:00.0 eth1: igb: eth1 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX
2021:03:07-12:30:37 lyneutm kernel: [317342.268650] br0: port 1(eth1) entered forwarding state
2021:03:07-12:30:37 lyneutm kernel: [317342.268669] br0: port 1(eth1) entered forwarding state
2021:03:07-12:30:38 lyneutm kernel: [317343.355436] igb 0000:02:00.0 eth1: igb: eth1 NIC Link is Down
2021:03:07-12:30:38 lyneutm kernel: [317343.355497] br0: port 1(eth1) entered disabled state
2021:03:07-12:30:41 lyneutm kernel: [317346.311117] igb 0000:02:00.0 eth1: igb: eth1 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX
2021:03:07-12:30:41 lyneutm kernel: [317346.311378] br0: port 1(eth1) entered forwarding state
2021:03:07-12:30:41 lyneutm kernel: [317346.311397] br0: port 1(eth1) entered forwarding state
2021:03:07-12:30:56 lyneutm kernel: [317361.353523] br0: port 1(eth1) entered forwarding state