Don't think there's a limit in the software. I use portable 5TB drives and they have been fine. I haven't tested my 10TB backup drives, but think it's a non-issue (assuming it's a drive file system that it supports)
NTFS for me works, and I have been fine with 5TB, 10TB, and 14TB drives (mainly Western Digital Elements / EasyStore externals). Try a different USB cable if have one handy (it sounds like it shouldn't work, but it did with me after a tip from another forum member). Original non-working cable then worked after switching back (I had other similar cables from other drives for spare to test). Otherwise specifying exact models that have problems could possibly inform on what any future firmware updates / fixes there might need to be.