Ah, I see now that it's about TW. Hm, interesting why it doesn't work. At the last time I tried RPi3B+, it worked fine with 4.18.5, and basically the fixes in Leap 15.0 KOTD is backports from the latest upstream. So I'm not sure what got broken for now. In anyway, you can try to blacklist microchip module. This phy module caused a problem on Leap 15.0 kernel, at least.