If you are doing challenge correctly then it can be linked issue. You have to link Trailhead to salesforce.
Follow the below instructions.
Please check if you have connected to same DE org where you have done your work in the trailhead.To do this click on" launch your hands on org" and select the DE org or trailhead playground where you have your work and then check challenge.
OR
Go to Trailhead Profile -- settings -- make the DE org which you have worked as default then check the challenge.
Please refer below link how to take challenges in trailhead.
If you are doing challenge correctly then it can be linked issue. You have to link Trailhead to salesforce.
Follow the below instructions.
Please check if you have connected to same DE org where you have done your work in the trailhead.To do this click on" launch your hands on org" and select the DE org or trailhead playground where you have your work and then check challenge.
OR
Go to Trailhead Profile -- settings -- make the DE org which you have worked as default then check the challenge.
Please refer below link how to take challenges in trailhead.
https://force.desk.com/customer/portal/articles/2643793-trailhead-profile-signup-login-faq?b_id=13478
Hope this helps you!
Please mark it as Best Answer if my reply was helpful. It will make it available for other as the proper solution.
Thanks and Regards
Arvind Kumar