Sweeps and Special Ground elbow?

Hi,

I've only noticed this a couple of times. So when I elbow the head in an online match or in practice mode from any top position, my opponent automatically traps my head down so I'm out of the postured up position. However twice I've been finished online  when someone has thrown an elbow to my head as part of a postured up G&P combo while I'm on bottom and they have remained in the postured up position, able to continue landing postured up G&P. Both times it has happened it has been in half guard. I've tried everything I can think of in Practice Mode and I can't replicate this. Much appreciation in advance to anyone that can help with this.

Second thing; I often get swept when in top side control or half guard into bottom side control or half guard. Sometimes it looks like a static sweep but mostly it looks dynamic and seems to happen when I'm trying to transition or punch / elbow. Again I just cannot work out how my opponents are doing it and how to deny it if indeed it is deniable (are they just racing it when I'm mid transition / strike? Is it to do with GA?). Sometimes I do it myself when I'm mounted and being pounded, I think it's some combo of R2, L1 and right stick that I'm hitting by accident while trying to block and pull the head down and I end up hitting all 3 buttons but I can't do it consistently. You obviously can't simulate this vs CPU in practice mode. I guess given all the above, my questions are; how is this sweep done, is it deniable and if so, how do I deny it?

Thanks again.