I am not an engineer, nor an electrician but will be happy to share my personal experience and what I believe may be causing the phenomena.
I think packs with internal solder tabs have such a short distance between the cells which use spot welds to get near zero internal resistance. When you...
True brand new pair of packs that can be matched will be perfectly fine to run all the way down to LVC.
Any other mix matched packs of varying brands and capacity can also be used for short periods of time, roughly 5 min or less... you don't want to risk going anywhere near LVC with mix matched...
I hate to be the bearer of bad news but this is a really bad idea... trust me,, been there, done that and I wasted a lot of money destroying a bunch of my packs when LiPo first came out and there wasn't any information sharing the do's and don'ts with series.
After I damaged 4 packs plus 1...