Bug Report: Ethernet disconnection issue(NanoPi R6C)

[somu1795]

What happened?

I did a fresh install from the latest ubuntu 24 build. I still see the ethernet disconnection issue. This issue was also present in the older build(Ubuntu 22). Sometimes(happens mostly when there's network I/O) the ethernet(2.5G LAN port) would disconnect automatically and reconnect back on.
This interrupts file transfers(or streaming etc) over network. The other port(1G port) does not get IP address.
The dmesg log says
RTL8226B_RTL8221B 2.5Gbps PHY r8169-3-3100:00: Downshift occurred from negotiated speed 1Gbps to actual speed 100Mbps, check cabling!
but the cable and router both are fine(I have tested with multiple routers and cables).

Kernel version

6.1.0-1024-rockchip

SBC model

NanoPi R6C

What operating system are you seeing this problem on?

Ubuntu 24.04 LTS (Noble Nombat)

Relevant logs

[   12.601351] rk_gmac-dwmac fe1c0000.ethernet end1: Register MEM_TYPE_PAGE_POOL RxQ-0
[   12.684187] rk_gmac-dwmac fe1c0000.ethernet end1: PHY [stmmac-1:01] driver [RTL8211F Gigabit Ethernet] (irq=POLL)
[   12.684718] dwmac4: Master AXI performs any burst length
[   12.684729] rk_gmac-dwmac fe1c0000.ethernet end1: No Safety Features support found
[   12.684743] rk_gmac-dwmac fe1c0000.ethernet end1: IEEE 1588-2008 Advanced Timestamp supported
[   12.685101] rk_gmac-dwmac fe1c0000.ethernet end1: registered PTP clock
[   12.685636] rk_gmac-dwmac fe1c0000.ethernet end1: FPE workqueue start
[   12.685645] rk_gmac-dwmac fe1c0000.ethernet end1: configuring for phy/rgmii-rxid link mode
[   12.767510] RTL8226B_RTL8221B 2.5Gbps PHY r8169-3-3100:00: attached PHY driver (mii_bus:phy_addr=r8169-3-3100:00, irq=MAC)
[   12.964388] r8169 0003:31:00.0 end0: Link is Down
[   13.765185] NET: Registered PF_QIPCRTR protocol family
[   13.871242] loop5: detected capacity change from 0 to 8
[   21.314587] platform mtd_vendor_storage: deferred probe pending
[   22.830779] RTL8226B_RTL8221B 2.5Gbps PHY r8169-3-3100:00: Downshift occurred from negotiated speed 1Gbps to actual speed 100Mbps, check cabling!
[   22.830803] r8169 0003:31:00.0 end0: Link is Up - 100Mbps/Full (downshifted) - flow control off
[   22.830836] IPv6: ADDRCONF(NETDEV_CHANGE): end0: link becomes ready