Well… guess what?
I got myself an otg adapter,
and magically the xbox tuner operates fine when connected on the front usb port.
Tried both latest kernel & TBS/crazycat modules,
both work ok with DVB-T broadcasts.
Changing channels still skips frames for like 3-5 secs on change,
but other than that its ok.
Tuner is available after a restart and after waking from suspend as it should.
The backend is still missing signal info (per/snr/signal) but reception is good,
and TVheadend 4.2 finds all expected services, epg works ok too.
I didn’t have time to test the other tuners/modules combinations,
but I suppose it would be the same.
I can test if someone needs the info.
Sooo… there is definitely something funky with the rear usb ports on N2.
My immediate issue is solved,
but if a dev. is in the mood to investigate I can still provide logs with the 3 tuners attached to the rear usb.
I sincerely hope its a software issue that can/will be solved because I’m starting to lose my confidence on odroid hardware.