Like your other 2 questions on this forum it is very unclear to others what exactly is happening because when are are talking about "clips in the timeline" you probably are pointing at timeline EVENTS and also other things.
To be clear to others show here screenshots or a screenvideo of the problems you are seeing.

I cannot work out what you may be doing to cause your problem but try turning Off Auto Ripple to see if that helps

The problem is caused by dragging a video file into the timeline incorrectly, and placing it above/overlaying another existing video on the time line. This can also happen when clips are already in the timeline.

You should either delete and add each clip carefully to each "snap" point or move all the clips far right and then drag them to each "snap" point as shown in the picture in Step 2.

Reproduced your issue: (I am using pictures alternating from a black picture to a red picture, instead of other clips. Same method applied to video clips). I simply dragged my pictures into the timeline and then dragged them over each other. This will cause some weird fading or another transition if watched back in the current state.

Step 1 to fixing this: (spread out all clips on timeline by dragging them to the right of each other, they may get out of order, though, so I'd suggest deleting and re-adding all clips in order like below:)

Step 2: Drag the clips to the snap point of the last part of the previous video. It should jump to that and show a blue line between each video clip like in the picture below, when you are close enough: (doing this wrong, and overlapping them, will result in the problem in the first picture)

Step 3: Repeat step 2 until all video files are aligned correctly with none of them overlapping: