Some telecommunications stocks did not do as well as they could have last year, and J.P. Morgan thinks it knows why.

The bank said in an April note that some investors grew concerned in 2017 about returns — or the lack of them — on so-called 5G mobile network technology, which is designed to deliver faster data speeds.

J.P. Morgan analysts said they found "depressed valuation" for Chinese, Japanese, South Korea and Australian telecommunications stocks. Those markets are likely to be the first in the region to roll out 5G, according to the bank.

All told, companies in the Asian telecom sector underperformed the MSCI Asia Index by 18 percent in the 12 months to April 2018, the analysts said.

But the bank dismissed 5G concerns as coming "too early" and said many telecom stocks could be showing a disconnect between their current price and their actual value.

James Sullivan, head of Asia ex-Japan equity research at J.P. Morgan, told CNBC that the media attention being paid to 5G is significantly outpacing the technology's impact in the real world. Many of its uses are still theoretical because complementary technologies don't really exist yet.

"It's not really about faster download speeds," he said. "It's about internet of things, autonomous vehicles and things of that nature for which no one understands a monetization case for networks yet."