1. Version: 21H2 Build: 22000.675
2. Version 1.24
3. Single Line. I'm not sure that answers your question. If not, repose your question.
4. 100% 1920x1080
5. I have only four taskbar items: Thunderbird (Mozilla), Firefox, AB Commander (file manager) and NotePad++ When the icons are missing, they are all missing. That is to say, when they first disappear, they ALL disappear. I can only restore the icons one at a time by starting the app by clicking on the empty space. That ALWAYS causes the icon to reappear.
I have not been able to identify any pattern regarding when the icons go missing. Only the taskbar items are affected; all others behave normally.
I hope this helps.