The accuracy not going below 10m was indeed an issue and was fixed in 1.14.0.
I highly encourage you to follow the Releases category so you are aware of changes made as they happen. You can do this by clicking on the circle in the upper right hand corner of the category page and selecting Watching:
I also highly encourage you to join the beta program with a test device. You can learn more about that at ODK Collect v1.14 Beta. ODK Collect runs on thousands of different kinds of devices in lots of different conditions so beta feedback is really important!
As for the XLSForm warning, it can be safely ignored.