Hi Otrhan,
In this case I changed the camera priors setting in a new project, added all my images and ran an alignmnent. Which was pretty good.
I then located the two GCPs and added 2 control points and set the measurement to 2m.
After a dozen or so more photos were aligned to the same 2 control points I got the error or warning message and I was seeing the distance value as 3m.
Paul