Try removing the .jpg from the rename token. So for your first upload you'd have:
"".$row_propid_for_ims['prop_id'] .""
and for your second one, you'd have:
"".$row_propid_for_ims['prop_id'] ."_[Increment]"
The renaming code that find a unique name builds a file name from this value plus the file extension of the uploaded file, and with the file extension in that value it was incorrectly determining the new file name.