Hey, I was in the same position as you, I did the assessment centre back in February and was in the matching process since then. I got matched to one role pretty quickly after AC but after telephone and face-to-face I was unsuccessful for the role. And then I heard nothing again about being matched to a role until about 2 weeks ago, so for about 3.5 months I was just in the matching process not getting matched to anything, although in that time I did keep getting that 'still matching you to a role' email. So I got matched to another role and through that I finally got an offer. They are still hiring for different offices so hopefully you do hear back from them very soon. I had pretty much given up hope and then out of the blue I got matched.
One thing I might say is try and be a bit more flexible with your preferences, at the AC I had put down South of England/London as my preference, so during that 3.5 months of being in matching process I expanded my preference to include Warwick and thats the office I eventually got in the end, so you can email the recruitment team and they'll change that for you. But also do apply for other placements just in case but i'm sure you are already doing that, I kept waiting to hear back from IBM and in that time I could have applied to many other places, so a lot of deadlines had passed when I finally decided to let go for a bit and apply elsewhere, obviously there were a lot less opportunities out there compared to start of 2016.
All the best, hope you hear back from them soon.