Go to Apps > PicManager > Settings and check the matching settings selected for the upload. If you use customizable matching, make sure your image filenames correspond to the selected criterion: product title, SKU, barcode, or URL handle.
Check the match type: if the Full match is selected, the image filename should fully correspond to the SKU, product title, or other identifier you’ve selected:
Finally, during the match, make sure you have finalized the upload by clicking the Finish Upload button: