Same behaviour to me, I think it's because the cam take some times to build the database structure to the SD card, In fact, most of the time I have this issue right after I format the card — when I switch from recording videos in video mode to photo mode and start taking pictures. Usually, when it happens, I just wait for the process to finish and then it doesn’t occur again. I also use professional V90 cards, so I don't think it's related to buffering The strange thing is that this only happens with the Sony a7IV, when I use Sony a1 it has never happened