Some cameras and external recorders use older versions of filesystems which have file size limitations that are a bit out of data for todays content. To work around that, they split a clip into what is sometimes a huge number of subclips. One that I regularly use is the Odyssey 7Q+ in combination with the Sony FS7 camera in 4K mode. At that resolution it can only store 40s of footage per file before it has to create a new subclip.
I've been using the Odyssey 7Q+ as an external recorder for quite some time and with much success. The reasons for using it are a separate conversation for another time.