Problem with updated firmware

My phone is a K750i. Used XS++ to update, originally was R1BC002, updated to R1DB001, using Main China CL Red CID49. Everything is fine, except for a small quirk. After upgrading, 2 days later I realised that my camera was not working. When sliding back the lens cover, it would flash to the camera screen for a second before going back to the main screen. When trying to access the camera through the main menu, it doesn't load at all. So I downgraded to R1CA021, but it still has the same problem, only that it happens after I use the web browser. If I turn off and turn on my phone again, it works fine.

Is it the firmware problem? Please help.