Actually, I think I found one of the most common reasons.. It's small pumps and dumps, created by crypto channels.

I analyzed the candles on a minute basis before the signal (green), at the moment of signal (blue) and after (red).

Check out the screenshot:

https://snipboard.io/manWZG.jpg

You can see that it has very low amount of trades. Then:

The organizers buy some of the coin

Send the signal at 18:02

Dump the coin

This happens lots of times per day. Even though I am not sure this is the only reason, but it seems like a common one, since there are tons of signals channels.