At this moment Adobe Mixamo Team working on updates. There are some workarounds that can help to solve rigged problem with using charachters from Mixamo.
1.Dn OBJ export crashes rigged properties of character model. Try to import Dn exported obj into PS and then export new obj from Ps for uploading into Mixamo. Do not use Face expressions for rigging that models in Mixamo. Some time that properties crashes rigged process.
2. You can download any rigged character from Mixamo and use them without any problem.
3. Create character in Fuse and save them into CC Libraries. Dragging them into Ps allows to rigged them directly in Ps and also use Face Expression. Also you can drag them from CC libraries directly into Dn
4. Characters that are exported from Dn can't be rgged in Mixamo at this moment.
Fo any opther question regarding Mixamo character please check Fuse forum where you can find more converstions concerning your Mixamo.https://community.adobe.com/t5/fuse-beta/bd-p/fuse?page=1&sort=relevance&filter=all