Mixin Messenger uses Coinmarketcap API to display assets' price. And it also displays the assets which are traded on OceanOne over 10 dollars for 1 hour. Therefore, some assets get prices on your wallet for some while, and then the prices become 0 again cause no sustaining trading volume on this platform.
*What is OceanOne? This is a decentralized exchange based on Mixin Network; if you like to visit it on the browser, you could visit the site https://ocean.one
If you like to trade through Mixin Messenger, please add Mixcoin (Bot ID 7000101524). The transactions between Mixin Messenger and OceanOne are free and instant too.
The common assets that suddenly get prices:
Asset key: 0xec2a0550a2e4da2a027b3fc06f70ba15a94a6dac
ONE（It's the native token of the exchange BigONE, not listed on coinmarketcap yet）
Asset key: 0x946551dd05c5abd7cc808927480225ce36d8c475