[I’ll help you to recreate this bug (you may need to try it a few times in one timeline because it only occurs sometimes and it is not a rendering issue, it doesn’t show up in the player itself]
How I add subtitles to a video:
File>Open other>Color>(select transparent color)
place it above the video clip, add “Text: Simple effect” and Wa-Lah! You have have your text and it sometimes doesn’t show up with the “Fade Out Video” effect with “Adjust opacity instead of fade with black” (screenshot(s))
it only seems to affect the transparent color thingies, all the emojis in this ~6 min edit are visible
as I said it can be fixed by disabling and enabling it but I didn’t notice it and it kinda messed with my video but whatever
the fix to this would be to use the “Opacity” filter instead, haven’t tried it yet but I think it should fix the problem for now until “Fade Out Video” gets fixed.