Some of those coins have such a low market capitalization that they become really easy to manipulate. Even with a few dollars you can make the price go up 1%. That's why I recommend you to only invest in coins with a marketcap above 500k use! I guess these are some examples? There are also groups outside there doing so called "pump and dump" together. They arrange that everybody starts to buy at a specific moment, hoping other people (outside their group) start to buy these coins to and then when everybody is buying, they sell. But watch out, the people organizing this already are selling while they say the group needs to buy! A lot of scammers out there!