Emojis for reactions (and in popups) got broken

Since a few days, the list of emojis in "reactions" stays empty for me. I tracked it down to the fonts used: none of them are available on my system. 3 are proprietary and thus won't be available for Linux (the Apple and MS ones), the fourth doesn't work on my distribution (support for colored TTF seems to have been added only recently; I'm running on an LTS still supported until 2021 that cannot deal with the Noto Color Emojis). Somehow, the spreadsheet fallback doesn't kick in either.

All worked fine until a few days ago, so some recent change must have broken it. Can you please verify and correct? If you need something to check with: Linux Mint 18.3 is what my machine currently runs. Due to some dependencies still unsolved, I cannot yet upgrade the system (and shouldn't have to just for some emojis 😉 (<- oops, that one stays blank for me as well in the popup – but shows up fine in preview, and probably also after posting this comment)