I have the same issue with the Netgear R6220:
[311768.306053] mtk_soc_eth 1e100000.ethernet eth0: port 3 link up
[326308.563468] mtk_soc_eth 1e100000.ethernet eth0: port 3 link down
[326311.227446] mtk_soc_eth 1e100000.ethernet eth0: port 3 link up
[337893.023836] mtk_soc_eth 1e100000.ethernet eth0: port 3 link down
[337896.867296] mtk_soc_eth 1e100000.ethernet eth0: port 3 link up
[341279.270143] mt76x2e 0000:01:00.0: Firmware Version: 0.0.00
[341279.281642] mt76x2e 0000:01:00.0: Build: 1
[341279.290039] mt76x2e 0000:01:00.0: Build Time: 201507311614____
[341279.318453] mt76x2e 0000:01:00.0: Firmware running!
[341279.338533] ieee80211 phy1: Hardware restart was requested
[342852.173685] mtk_soc_eth 1e100000.ethernet eth0: port 3 link down
[342854.857630] mtk_soc_eth 1e100000.ethernet eth0: port 3 link up
[349963.279376] mtk_soc_eth 1e100000.ethernet eth0: port 3 link down
[349965.967635] mtk_soc_eth 1e100000.ethernet eth0: port 3 link up
[351498.704203] mtk_soc_eth 1e100000.ethernet eth0: port 3 link down
[351502.654127] mtk_soc_eth 1e100000.ethernet eth0: port 3 link up
[360266.776839] mtk_soc_eth 1e100000.ethernet eth0: port 3 link down
[360269.332901] mtk_soc_eth 1e100000.ethernet eth0: port 3 link up
[364880.383706] mtk_soc_eth 1e100000.ethernet eth0: port 3 link down
[364882.984503] mtk_soc_eth 1e100000.ethernet
Running 19.07.4 did solve my issue when unplugging a USB 3 gigabit controller it disconnected some ports.