Hey Harry,
I've never had any problems using the overlay feature in the hundreds of laps I've used the App if you don't count the watermark thing that is

Anyhow, none of my laps from yesterday will overlay properly. One of two things happens. My fastest lap, which I tried to overlay first, went through the usual rendering process and was on the final step of "transfering video to library" but it staid stuck on that step for over 10 minutes. I closed laptimer and tried again, same thing. I closed every app on the phone and did a hard reboot, still same problem. I then tried some other laps from that day and they all look like they work. The transferring to library part takes about as long as expected but when it finishes and I go to my library there is no new video with the overlay. I've tried this over and over with many reboots, hard reboots, etc.
This was my first time at this particular track so I'm really hoping to use the overlay feature!
Thanks