You probably used your texture from element 3d itself.
How to solve this?
- Import your texture to comp
- Precomp and name it say "texture 1"
- In element 3D solid, go to "custom textures" and in custom slot choose your previously made "texture 1"
- Open element 3d, click "setup".
- Choose your element model and choose for example "reflection" slot then add in thhat slot custom layer - texture 1
This way, you’ll always have your textures saved when you export/collect project.