UL_TBF_drop due to N3103 (ALU B11)

Good night, dear GSM experts!
Good night, dear Alcatel gurus!
Good night, dear dear Pix!

Being back to my work, I face a new problem 🙂
I’ve noticed that there are a lot of cells with abnormally high UL_TBF_drop_rate – more than 25-35%. Mainly all those drops are due to N3103 counter expires (i.e. becomes more than N3103_limit). This case belongs to radio problems, but I can’t find any obvious or reasonable explanation for such situation:
– there are no problem with coverage
– no interference (at least significant – to cause such UL_TBF_drop_rate increasing…)
– all other KPIs are good (either PS or CS)
– for each cell I can find the date when the problem began. As usual it happens abruptly and without any other symptoms (alarms or other KPIs deterioration)
I think it’s not a real radio problem because if it’s so we should face both N3103 and N3101 KPIs deterioration, shouldn’t we?
And my questions:
1)How do you think, could it be some terminals which act incorrectly when they finish UL TBF?
2) In our network N3103_LIMIT = 1 and it is according to recommended rules (in OMC-R help).
What is the danger if we break this rule and set another value for N3103_LIMIT? And which value we should try?

Many thanks in advance.
BR, Lily