A module cannot have multiple default exports
Quick Way
As sometimes you can just reopen a file as stated in other answers, it doesn't always help, however.
Update: Dec 10, 2020. The previous option (see below) is not available in new versions of WebStorm. To restart the TS service now, you can use the following option:
See more details on TypeScript tool window help center page.
Previous functionality (prior versions)
When you see lags like this one (and other weirdness from TS service), you can restart the TypeScript service by opening a TypeScript tool window and clicking on the "Restart" button (3rd button on the right side of the panel):
I had the same error. After restarting WebStorm it worked again.