I'm still a beginner with custom UI designs, so if this might seem a silly question, please bear with me

I wanted to make a transparent UI dialogue, but whenever a dialogue closes, I can see for a short moment the text the NPC said before. How can I immediately remove the previous text so that no text is below my current text?
Attached a video of what it looks like:
As you can see, the NPC text (Bruuu bruuuu) is visible for a very short time when the only possible answer was selected by the player, it looks like it overlaps.
These are my current settings for the Dialogue Manager in general:

I thought that perhaps the setting "Show NPC Subtitles with Responses" might solve the problem, but it stays the same.
My custom UI is a copy of the focus template.
All the best,
Evelyn