As you can see in the picture I have 13 out of 5. But it's been like this for about 2 months! What's the reason for that?
No bug here.
The Curious badge has two criteria to be awarded:
- Ask a good question on 5 separate days
- Maintain a positive question record
You did fulfil the first, on 13 days, and that is what you see, but failed the second. It's even clearly stated in the profile when clicking the "Curious" badge in there:
This other answer by Robert covers the whole aspect of why you failed that second criteria and how to fix it.
You could try improving them and then undeleting them to see whether you can rescue them. Alternatively you're just going to have to ask more good questions to balance out the deleted bad ones. See this answer for more details on the calculation.