U.S.-China trade talks in London this week are expected to take up a series of fresh disputes that have buffeted relations, threatening a fragile truce over tariffs. Both sides agreed in Geneva last month to a 90-day suspension of most of the 100%-plus tariffs they had imposed on each other in an escalating trade war that had sparked fears of recession. Since then, the U.S. and China have exchanged angry words over advanced semiconductors that power artificial intelligence, “rare earths” that are vital to carmakers and other industries, and visas for Chinese students at American universities.