I signed up this forum to reply to this post. Before update 3.15 I never experienced any lockups. Unfortunately right when I updated to 3.15 I bought a BT headset for my phone and use it consecutively with my classic Sixaxis controllers. These are the original, no rumble, Sony Authentic controllers.
Lately I have experienced the lockups on almost all of my 4 controllers. It is as you describe exactly: 4-5 seconds, usually involves holding down the directional pad. I haven't had any of the buttons remain pressed / locked.
I am extremely interested to hear if you've solved this issue. I have not been able to. When the BT is off on my phone the lockups don't *seem* to come, but it may be I didn't play long enough to re-enact them, or I wasn't playing a controller intensive game where it would matter.
PS: I'm almost 100% sure it's BT disturbance though. It may be that the older controllers don't send a strong signal or are more prone to radio disturbance. Whatever it is, it seems that when I have the BT headset on it's got a higher chance for freezing.