In my experience, with our Finders, that is a error based on corrupted data over WiFi. It’s happened so much for me that I stopped using that function all together and went with 3D Printer OS on a Raspberry Pi or just plain old USB flash drives. And, as far as I know, Flashforge uses FAT32 file system and can handle up to 2GB file sizes, so it can’t be that, unless your trying to print at 0.0125mm layer height and 20mm/sec on the max build volume with crazy infill and support, I don’t think you would ever have a file size that large for a single print.
Also, the internal memory of the Finder is a microSD card plugged into the mainboard. I have had to replace them with fresh 8GB cards, although very rarely.