Web panels for Gmail and Google Drive don't display their favicon until after the desktop version of the site is loaded...
...and Dropbox web panel doesn't display until the panel is opened. Vivaldi forgets the favicons after a relaunch.
Before I load the desktop versions of Gmail and Google Drive, and before I load the Dropbox web panel:
I am on Manjaro.
Yes, the bug with missing icons in panels is already reported.
No solution yet.