Navigation - Mega Menu

Hello,

I have SharePoint as my company's intranet and have 4 main sites (Company (Hub Site), HR, Marketing, IT). Today I am set to release our Training Department. All are communicate sites and HR, Marketing, IT, and Training have the Company site listed as their hub. The Hub site has the mega menu selected for global navigation. I added a link to the Hub Site navigation called Training and it will navigate to the Training site. However, when I go into any document library in that site the Training link disappears.  I have disassociated Training from the Hub site and re-associated it with no change. I have cleared my cached and have checked other users and have the same result. I don't see any health issues listed for SharePoint. This one baffles me and I would appreciate any insight anyone may be able to provide.