MSM not showing one of my sites in CP

Hi All, One of my sites is not showing up in the dropdown menu in control panel. The site is working properly from an end user point of view, but ever since I have upgraded to EE 3.x, I can not modify it in the CP. I have 3 total sites in EE’s DB, and I use two of those sites (one site is no longer used). All of the sites are residing on one virtual Linux server. Thanks for any advice