Camera lens automatically out of focus

I'm using AXIS p 1435-E with NUUO main console. The camera was working properly without any focusing issue at the beginning. But after a few weeks it got out of focused, resulting a blurred view. Then I focused it simply using the auto focus function. It was focused and worked for a few days. Again it got out of focused and I focused it using lens calibration and auto focus function. But this thing happened for three or four times frequently and then I upgraded the firmware with the latest one. Then it worked for a few weeks more and again started the same problem. This camera is powered by a PoE injector. What could be the reason for this matter?

Check for cobwebs or similar on the lense.

I had similar problem once, and a spider had decided to live by the nice, warm camera house.

Everytime the spider went for a walk it disrupted the image.