Solid red light on a few GFCI outlets. Sooo, what exactly does that mean? Outlet worked/tested/tripped/reset just fine. TIA.
Means there is a shelf in front of and blocking the photo-voltaic trip sensor! 
Oh, btw… (may vary by manufacturer)… https://home.leviton.com/blog/facts-about-your-gfci-status-indicator-light/
RTFM provided by the manufacturer