Quick Way
As sometimes you can just reopen a file as stated in other answers, it doesn’t always help, however.
When you see lags like this one (and other weirdness from TS service), you can restart the TypeScript service using the following way:
See more details on TypeScript tool window help center page.
Previous functionality (prior versions)
Restart TypeScript service by opening a TypeScript tool window and clicking on the “Restart” button (3rd button on the right side of the panel):
