Disable SSIM filtering for shifts in the subpixel range or add a tolerance.
For shifts in the subpixel range, it may happen that the SSIM decreases after correcting the detected misregistration. In many cases this is only caused by the resampling and there is no reason to flag the respective tie point as an outlier.
A solution could be to disable the SSIM filtering for all tie points with shifts well in the subpixel range or to add some tolerance when comparing the pre- and post-coregistration SSIM. This way, the RANSAC filtering can still be turned on - otherwise it is also turned off when disabling SSIM filtering via the input parameters.