Boxed questions marks everywhere
I've asked this question before with conflicting replies. I'm running a MacBook Air with Safari, Pages, Numbers, etc. All are up-to-date according to Apple.
MacOS Mojave v10.14.5 Darwin v18.6.0 kernel
System report shows that valid, enabled fonts for all the True Type, OpenType, and Postscript in /Library/Fonts
I'm getting boxed question marks in virtually all text: Apple diagnostics, Apple Activity Monitor, websites, Pages documents, and the like. Some text appears, some do not. Refreshing a page may change what is legible; or more likely, not. I'm not running Fusion Suitcase or anything else like it. I've followed instructions to FontBook (remove duplicates, re-load standard fonts, etc.) with no apparent effect.
MacBook Air 13", macOS 10.14