Hope you all are doing well...
Unfortunately for me I may have a case of this syndrome myself (though I have perfectly good reasons!
I had to leave my dojo in San Francisco a few weeks after attaining 2nd Kyu. I've have been away from aikido for just over a year now (married, moved, now commute) and there is a definite gap in my life, I must return to the art as soon as the situation allows.
I hope I avoided the two problems you mentioned during the course of my training. While I was training in SF I was a full-time grad student and I was able to spend much more time at the dojo than I did on campus. I always had a great time with the people I trained with. I did get bored on occasion, but I attribute that more to burn-out than anything, so occasionally I would take a week off to clear my mind and let my body rest.
I really hope I avoided the ego problem. My dojo was predominantly yudansha. Everyone else was either my level or near it or super-beginners (where I could feel justified slightly adjusting their technique). I always felt like a student, and in no situation to teach anyone anything, and was perfectly satisfied with that. It helped that there were lots of black belts to correct the beginners so I never had to anyway. I can imagine there might be a problem with the brown-belt syndrome in a dojo with a broader cross-section of student levels and less senior students.
If I had been able to stay at my dojo in SF, I can't imagine taking large amounts of time off, my friends were all getting their shodans and that is a real goal of mine. It could have been attainable fairly quickly if I kept my regular training schedule. Now that goal has shifted much further down the line, and I have come to yearn just for the act of training at all, even if a black belt isn't in the immediate future.