I am a Certified Information Technology Researcher, Developer, and Engineer. I too purchased the S5 Active, specifically the SM-G870ACPro with Qualcomm Adreno 330 and Quad Core 2.5. I also had the Focus Problem. My phone developed the issue at 24 days into use. I got the warranty replacement, which I received the next day under priority shipping, and am upset that it was a refurbished phone. However, maybe it is a good thing. Maybe I received one which had already had camera hardware replacement and it will keep hold. I noticed my phone getting hot at first.
I pulled out my Camera to take some shots of my newborn daughter, and it wouldn't focus on anything further than 3 inches away. No film over lens, so do don't bother. No scratches, no falls, drops, etc on this Military Spec. Shock Resistant etc. phone... Factory reset, pulled the Samsung SDHC card, tried again. Nothing. So I filed for the warranty. Next day during work while using the malfunctioning phone, my leg got extremely hot. I pulled it out of my pocket, and the LED Light, the Flash, was steadily lit up. I figured my toolbox had got opened and flashlight turned on. Nope. I turned it on and off anyways, no response. So I then proceeded to open the Cam and attempt to use flash. Then I finally got the "Warning, Camera Failed" message, and everything was black. I tried this multiple times, checked tracking, and my new phone was already at it's destination. So after work I switched phones, packaged the bad one, mailed it, and done with it for now. I have the ATT Variant. ATT told me they have not received complaints or tickets under this issue yet. I say they are trying to cover the flaws.