Missing Fonts Message In Illustrator Not Displaying

The solution is simple

Edit>>Preferences>>General>>"Reset All Warning Dialogs"

Thanks for sharing the solution. 100% working.

What OS and Illustrator versions are you using?

Are you using a font manager to auto activate?

Is this usually the same font, if so which one(s)?

Do you never get font warning, or only once in awhile you open a file , have some pink highlighted type, and go to find font and find you have  missing fonts.

Fonts can  be quite complex, so will need more information to give you a better answer. If you have a lot of old type 1 fonts, they can cause this. Also a conflict of 2 fonts fighting to take on the postcript name that Illustrator is ending to the OS to open can.

In general preferences you can try to reset all warning dialogs or

Reset Your Preferences.

Cmd-Opt-Ctrl-Shift when restarting AI on a Mac or Alt-Crtl-Shift on a PC to reset to the defaults.

More Thorough Reset Your Preferences.

Quit Illustrator

Finder >> Shift Command G

~/Library/Preferences/Adobe Illustrator 21 Settings/en_US*/Adobe Illustrator Prefs

rename Adobe Illustrator 21 to Adobe Illustrator 21 old

Reset Your Other Preferences

Quit Illustrator

Finder >> Shift Command G

~/Library/Application Support/Adobe/Adobe Illustrator 21/

rename Adobe Illustrator 21 to Adobe Illustrator 21 old

Press Win+R -> appdata -> Roaming -> Adobe -> rename folder Adobe Illustrator 20 (or 21) Settings to any other name.