I have georeferenced some aerial images, loaded in QGIS and saved them (files .tiff, aux.xml and .points). These images overlap, however I found that some details in the borders did not match exactly after georeferencing (perhaps due to the lack of GCPs - I am using TPS transformation). Since I am building a mosaic, I wanted to add a few more GCPs to improve the precision and match the elements in the borders of these images.
In order to do so, I reopened Georeferencer, loaded the unprocessed image (.tiff file) as well as the GCPs previously created (.points file) over that same image. The red GCPs showed on the Georeferencer window, but not on QGIS. When added extra points, they showed on both windows, but I noticed that the calculated residual values disappeared (became zeros) in the GCPs table. From what I understand, no residuals means no georeferencing process. When trying to load the raster into QGIS, there are no error messages, only a grey rectangle on a strange scale, different from the projects CRS.
Is this procedure (adding/editing previously saved GCPs) even possible? What I am doing wrong?