Steps to produce:
  1. Launch Unity with 3.7.6 SDK
  2. Load your world
  3. Upload Android version
  4. Test it works = Works
  5. Upload iOS vesion
  6. Test it works = Works
  7. Join again with Android = World will not load nor pre-load
Currently, the workaround is to upload the Android world again. But this happens always if you upload iOS world right after.
Edit: World ID in question: wrld_6f12cc23-872d-40f1-8c1a-ad1682b92c97