I don't have 995, but after frequenting this forum for so long I can tell you that the carbines are the ones with the fewest problems.
As NarcoticRex asked, have you installed the ATI after-market stock, or are you using the OEM stock? That may be the culprit, or just aiding the problem.
Now, the problem occurs only on the 2nd round? There are no other times that you can recall having this type of malfunction on another round in the sequence? That seems a rather odd place to only have a failure. I am by no means doubting you.
You also are saying that you have too much space between the bottom of the mag-well and the mag, and that it is a factory mag, not the 15rd Pro-Mag. Correct? Does the mag move only up and down? Only side to side? Or is it all over the place?
Have you experienced this malfunction with other brands of ammo besides Blazer Brass? My C9 eats only BB when she is at the range, and the 995 is basically a C9 with the extra parts added to make it a carbine. Therefore, I know BB has enough power to handle cycling the slide. Some firearms, even the top of the line models like Hi-Point (

), can be picky about what brand(s) they are fed. My C9 doesn't like Wolf or Blazer steel cased, my Dad's does. His C9 doesn't like WWB, mine does...well did, anyway. It could just be that your 995 doesn't like BB and chooses to tell you on the 2nd round of each mag.
If the mag catch was the culprit, I would think that the malfunction would occur every time the slide cycles automatically, not just on the 2nd round. I believe it would occur on the 2nd, 4th, 6th, 8th, and 10th, or, basically every time that you didn't manually cycle the slide.
How many rounds have you fired through your 995 thus far? Even though the carbines do not have as many problems, they do still, more than likely, have a break-in period. For the pistols the break-in period is anywhere from 300 to 800 rounds.
One last thing. Do you have more than one mag? If so, does it happen with all of your mags? Have you marked your mags to find out if it just one mag or which mags it occurs with. If you only have one mag, have you tried another mag? Maybe a friend's, acquaintance's, or even enemy's mag that you could borrow? Try purchasing another mag from
www.hipointfirearms.net, and if you don't have any problems from the new one, then send the old one in for replacement.
Lastly, if it does turn out to be the mag release, you will not need to purchase it. If you feel comfortable replacing it yourself, they will simply mail it to you free of charge. If you are not so confident and feel that it would be better for Hi-Point to make the repairs, then all you will need to pay are the shipping costs to their plant. They will make the necessary repairs, test fire it, and send it back to you, more than likely with a free mag to offset the cost of the initial shipping.
Good luck and sorry for the book. I hope it helps. Also, Please be patient with your Hi-Point, they truly are great firearms.