We regularly see cases of APFS filesystem corruption that lead to errors during a backup task. This corruption is typically presented in an error like one of these:
readlink_stat("/Photos/Foo/2020_Dumpster_fire.jpg") failed: Illegal byte sequence (92)
rename("/Photos/Foo/.2020_Dumpster_fire_out_of_control.jpg.asdfgh" -> "/Photos/Foo/2020_Dumpster_fire_out_of_control.jpg") failed: No such file or directory (2)
When CCC encounters these errors, the affected items are listed in CCC's Task History window, often with this advice: