I have a server with routeros 5.11 (same with 5.14), which eventually locks up hard if built-in ethernnet is used.
0 device="04:00.0" name="RTL8111/8168B PCI Express Gigabit Ethernet controller (rev: 6)" vendor="Realtek Semiconductor Co., Ltd."
category="Ethernet controller" vendor-id="0x10ec" device-id="0x8168" irq=5 memory=0xFBDFF000-0xFBDFFFFF,0xFBDF8000-0xFBDFBFFF
io=0xCE00-0xCEFF
Probably it is related to these linux kernel reports:
https://bugzilla.redhat.com/show_bug.cgi?id=654147
https://bugzilla.kernel.org/show_bug.cgi?id=32962