In order to keep compatibility with Macs, which can't natively read and write to the superior NTFS file format, camera makers use the FAT32 format for the cards used in recording. FAT32 only allows 4GB files, so any time you have a longer clip, it gets broken up into multiple files. This is called 'spanning'. PP understands this and shows you only the first file of that one clip. The 'missing' files are the rest of that clip.
Hopefully, future cameras will allow the use of the newer exFAT format, which newer Macs can natively read and write to, and which allow much larger file sizes. This would mean one file per clip, no more spanning.
Please do write a letter to Canon expressing your desire to use the exFAT format in their cameras.