Set the time to around 4am and search for C/2020 R4 (ATLAS). It's Mag 9.8 at the moment and shows up as a symbol for me.
If it finds it and shows the label, at least you know that the data is there and it's a display/symbol related issue.
I can find Halley at Mag 34.9. It shows a label (if it's above the horizon) but no symbol.
Also, in Setup/Solar System/Comet/General Settings are some display settings that you may have overlooked. Show comets on chart and show comets X magnitudes fainter than stars. If you've wound the stars back to just show bright ones, you may not meet that criteria to show comets.
I have the value set at 4 magnitudes fainter.