it has been always an issue but until now there are no concrete documents and proofs about how it works and who are manipulating the market.
though it is really looking as is when the market is pumping without any good reason same as when it was dumping.that is why we can't take from our minds to think that manipulators are on the go.but investing is a risk so better expect some losing than total winnings.
Actually, you don't need any documents or evidence to answer the question if the market is manipulated or not. You said yourself that at some moments you can notice very fast price jumps or its declines. This is manipulating the market to trigger panic buy or panic sell.
Badly it was as people think and it sometimes manipulation seems to happen in all areas. Crypto is a big market and this will able to give chances for influential people to take advantage of the market. It can't be of really visible to us but it actually happens in reality.