I am wondering what those issues are? In Syria for example, a Turkish drone took out the system while the radar was active! One of the two, the system failed to detect the drone because of its size or because the drone was flying on a very low altitude. Both ways put a big question mark on the effectiveness of the system preforming as SHORAD. I think this justifies why Russia introduces a new version of the system with enhanced radar?
I will try to explain.
Just because a radar is active, it does not mean the system is armed. When armed AND on auto, the system will automatically neutralize any threat, other wise "man behind the system" becomes the issue.
Now there are a number of reasons, why even this would not work, one is that the incoming a/c is using terrain to hide itself, thus popping up at the last minute and neutralizing the ADS (Air Defense System). This is one reason, why ADS are placed, at possibly the highest point in a sector.
Another reason is that, a secondary a/c might be jamming the radar, and confusing the ADS.
There is also an inherent flaw with short range ADS. Their radars, anything less than AESA is "comparatively" easy to jam. A cheaper way of addressing this issue is to introduce an new variable into the equation, i.e. eclctro optical tracker, No.7 below. Then again, there are ways of confusing it as well.
So the best way to neutralize drone level threats is to have APKWS
The Advanced Precision Kill Weapon System (APKWS) is a laser-guided 70mm rocket system manufactured by BAE Systems in collaboration with the US government.