Just upgraded to 12.3.1 and now unable to import video files from SD card

Prior to IOS 12.3.1 I had been successfully using a flash cable adaptor that connects a micro SD card to my Ipadpro flashport in order to import pictures and videos. I record the videos in the SD card using the GoPro Hero 7. Since upgrading to 12.3.1 I can no longer import videos this way. The import function seems to be working bur after a period of time a small warning exclamation mark pops up over the thumbnail of the video I am attempting to import. I have tried importing to the iPhone and to an older iPad, all with the same result (they were all recently upgraded to iOS 12.3.1).

is there anything I can do to fix this or does this need attention by Apple to implement an iOS fix ?