Steps to reproduce:
- open an article for editing in 2017 wikitext editor
- open find & replace
- type in some word that shows up multiple times on the screen (scrolling seems to fix highlighting)
- close find & replace (this and the previous step are needed sometimes but not always)
- open find & replace with F3
Observe that the word is not highlighted. When you press escape, the word will become selected, so the selection logic works (and F3 advances the selection correctly) but selection is not visible while the find panel is open.
The same does not seem to happen when using Ctrl-F to open the panel.
Seen on Chrome 85 on Ubuntu.