If some screenshot files are not shown in Select Screenshot Image dialog, check followings.
FRep2 checks if the image file; 1. is either of PNG, JPG(JPEG), BMP type; 2. has the width and height are equal or larger than those of the device screen*.
[on Android 10~, some specific devices]
Try Data Settings – Disable Media Filter: ON in the menu of Edit Sequence.
[In case the issue occurs after system update of the device]
On recent Android system, standard apps cannot access the files in non-public location. First, confirm the public location of the device for the images (such as ‘Images/Pictures’ ) in Select Screenshot Image dialog, by tapping Change or long-tapping Up button to switch the base referring location. If the required files are not there, please use some filer app to move them to the public location.