Why is it incorrect to write tu ne tu perdras pas?
It should be "Que tu ne tE perdras pas". Accusative/direct complement second person singular is "te", while "tu" is nominative/subject.
That was my answer: que tu ne te perdras pas. It was rated wrong
▶ Tu is a subject pronoun, here you need a reflexive pronoun:
Why is this not accepted: J'espère que tu ne te vas perdre pas