Hi Ana,
I too have had the same problem. However, if I use ground control points and undertake camera optimisation with all cameras and GCPs 'ticked' Metashape is able to determine the true parameters of the camera (unfortunately the parameters in the XMP data within the image file is a guide at best). I then save this camera calibration data and then use it for all my projects (with a couple of check points just in case). Results come out very good indeed.
If this is unclear let me know and i'll try to be more descriptive.
Regards,
David S
CD Surveys, NZ