Ah that might explain it! They are indeed ancient characters haha. I'm finding a lot of errors with them probably because so many changes have occurred since they were created. (For example I don't get the crystals coupon and dust from the lv 2 rune quest and they had 60k worth of non expiring myrrh which when I right clicked to use, didn't go under the currency tab and completely vanished.)
Just as an addition. I think the lack of a mentor tab is a bug only for ancient characters who got to lv 9 or above. I had a few other ancient characters at lv 8 who were able to join the system after I leveled them to 9 this last week.
What makes it more confusing though is that I have a lv 33 character who does have a mentor tab (I believe all my characters were created at around the same time) and she actually transferred over with a pupil on her list already. She doesn't have the ability to gain a mentor though, only pupils. Is this normal for a lv 30+?
I'm not sure now if it's worth making a ticket about all the problems since it sounds like it'll be a massive headache. Probably best just to start over on the lv 15s >_<. Thanks for bringing this up. I hadn't considered it might be their age