I have 2 or 3 years with DJI Drones and shot a lot of 4K video and have never seen this behavior.
Can't tell you you haven't seen something you say you have, but you have the ONLY device (not just drone) in the entire world that somehow can store files larger than 4GB on the very old, MSDOS-originated FAT32 file system.
FAT stands for "File Allocation Table", a part of the overall file system structure that indexes the blocks of data in a file. FAT was originally developed in 1977 using an 8-bit index for the file storage, sufficient for indexing files on floppy discs, the state-of-the-art in small computer storage at the time. Over the next 15 years the design of FAT was updated to a 12, 16, and finally 32-bit index as storage technology grew.
FAT supports random access to the file with byte resolution using a 32-bit pointer. 32 bits can index 2^32, or a bit over 4B bytes. Therefore you can not index – point to, read, write, etc. – any byte in a file beyond 4GB.
Again, only you can speak to your experience. However, given that it is impossible for you to have stored a file larger than 4GB on a FAT32 filesystem, I can say with 100% confidence that you were hallucinating
BTW, I'll see your 2-3 years DJI experience and raise to 9 on my side, across Phantom 3, Mavic Pro, Mavic 2 Pro, Mavic Air, Air 2, Air 2S, Mini 2, Mini 3, DJI FPV.
I think across all those years, models, and hundreds of hours of sometimes quite sophisticated production turning that footage into amazing video I would have noticed NOT needing to splice footage.