According to How do suggested edits work? you can propose five edits at one time:
When can I not suggest an edit?
You have 5 suggested edits pending (20 on beta sites). Wait for one of them to be reviewed.
I found a way to propose six edits:
Edit 4 tag wikis/excerpts
Go to edit a tag
Edit both the tag wiki and the excerpt
You have six suggested edits:
Whilst when having five suggested edits you can't suggest anymore. Is this supposed to happen or not?