Repro steps:
1. Open the 15_SpriteTextures scene from the project attached in the comments below.
2. Select the particle system in the system and inspect the missing sprites in the Texture Sheet Animation model.
3. Select the 4 sprites in the Art/Cans folder and see that they are all sharing the same package tag.

Notes:
- works fine in 2018.3.0b11
- even though they have identical settings, the two missing sprites cannot be displayed when reassigned