Camera isn't available - Trusted Face ( Android Lollipop - Nexus 5) Sometimes I've noticed that the Smart Lock - Trusted Face feature doesn't work, no matter what the lighting or the position of my face relative to the phone. 

I thought that an "Improve face matching" should do the trick, but when I go to do that, I get this:


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Usually a restart fixes things, but this isn't a really good solution. The camera app works normally even when this happens. Has someone found a way to fix this somehow, or should I just wait for the next update from Google?
I believe that this is an issue with the Smart Lock app itself. When I enabled the face unlock I started getting this error. The camera ceases to work after some time, when I notice that the smart lock icon just blinks on the lock screen (which shows a failed attempt to access camera). Then neither the camera app works nor can I access the camera via Smart Lock settings. I started having this issue whenever I enabled face recognition and I stopped having this issue altogether when I disabled the said feature.

It's a shame that despite being an extremely efficient and fast feature, this causes such a problem that it needs to be disabled.