A large number of Gboard users are reporting that the spell checker feature - which makes sure misspelled words get underlined in red - is not working for them. Complaints are scattered across Reddit as well as Google own product forums.
Since November of last year, the red underline has stopped appearing for incorrectly spelled words when using GBoard. I noticed this with my Pixel on Oreo.
There's also a discussion going on about this problem over at Google Issue Tracker, and a quick look there reveals the company knows about the issue as info related to it was passed to the concerned development team back in January this year.
Here's what exactly a Google employee had said then:
We have passed this to the development team and will update this issue with more information as it becomes available.
However, there has been no update from the company since then. Understandably, most users - especially those who use their phones for business purposes (sending work emails and all) - aren't happy about the way Google has handled the bug so far.
Here's hoping a fix arrives sooner than later.