I've recently bought a Macbook Pro (13-inch, 2017, Four Thunderbolt 3 Ports). Out of nowhere, the letter "B" on my keyboard stopped working. Sometimes, if I have the keyboard viewer on, it'd work after pressing it for more than one time. Sometimes, it doesn't. I'm still not 100% if the issue is a hardware issue or a software issue. I noticed the issue after I upgraded the MacOs into Mojave. Any suggestions on what the issue is and how to fix it?