Canon Camera plays seemlessly its recording of severall clips. But not when imported on a timeline

Hello all, recently my friend video an event with a Canon video camera  (Legria HF S 20) and edited the files on many video editing program including PP2024. 
When playing  the whole recording on the camera it was perfect, but when importing the files on a timeline, the spot where the files were joined weren't smooth at all. Either produced a noise or a missing part of  a word occured!.  
This camera records only some 15 minutes clip then creates a new one.  
The files imported from the camera are like twins. One '.MTS' with a reasonable amount of bites but the other is a '.mts.idx2' with a much smaller amount of bites. Both with the same content before the first dot.

Like with PP2024 other pgr did not accept the '.mts.idx2' . 

We are wondering why this is happening