I still don't understand why this happened as it was working great for
years and is still working with kernels 6.8.7 or older. But
nevertheless sorry if I wasted time of anyone because of broken
hardware.
I think the BIOS CM creates the "first" tunnel using reduced
capabilities already so this makes the "second" tunnel fit there in the
18G link. Now that we do the reset the "first" tunnel is re-created with
max capabilities and that makes the "second" not to fit there anymore.
But now you get the full 40G link :)