Sounds to me like a mismatch between the kernel and the module. I couldn't find any kernel modules within the cpio archive or ubifs so my guess is that these are coming from the rootfs of Harmattan (is that right juiceme?). If this is the case, the new kernel probably differs sufficiently that it would cause the problem. One possible solution could be to bundle the newly built modules with ubiboot and mount them over the top the rootfs.

juiceme, what's the reason for the new ubiboot kernel? Has anything changed there? I never bothered to flash the new ubiboot kernel as the changes I submitted didn't require them so I'm still on the previous kernel (0.3.6 tiny) and have no problems with loading g_multi.

EDIT:
P.S. I haven't been able to get any recent (patched) mainline kernel to boot at all via ubiboot, not even by entering the kexec command manually via telnet. It's very difficult to debug without a serial console and can't find any info on how to build a cable for the N950 (I don't have an N9). One option I was hoping for was to build a ubiboot kernel with the serial USB gadget but as juiceme knows, it's broken and doesn't build right now.

My only (semi) success with booting patched mainline has been with Pali's 0xFFFF with the default (NULL?) kernel cmdline. With that I'm able to bring up initrd and the display comes up. The strange thing is that if I try to specify a cmdline, it breaks it.