I noticed there is a bug in QCAR which makes the scale of some markers jump to 60,60,60 in the editor if you click on one of the markers in the Hierarchy window. This behavior is rare, completely random, and I can't reproduce it. But I know it happens both on OSX and Windows.

I know this isn't of much help to solve it but perhaps you can consider this:
In the file SceneManager.cs, in the function GetFrameMarker, there is a line of code which looks suspicious:

//Initialize Frame Marker with default values if it is not defined in backlog.
fm.size = new Vector2(60.0f, 60.0f);

This is probably the culprit but it is still a mystery why this function is sometimes called while it shouldn't be.