This utility has an interesting approach to merging photo sequences - but unsure if EXIF --> creation date is an option or not... http://www.maczentrisch.de/shootShifter/
I have extended the life of several Macs by installing upgrades (RAM, SSD) from OWC (Other World Computing). Top notch equipment. Excellent video instructions on performing the needed surgery. https://eshop.macsales.com/upgrades/
Perhaps a hardware issue? Flash drives have a limited life. Can you use a different stick or validate they are working correctly from hard drive before copying them elsewhere?