Didnt get the forth artifact

Hi, i was playing on mission 16, beat THE boss and then a online player camed in, went in the vault and picked the 4th artifact and teleport to the sanctuary and logged out and I continued played, now i noticed thats were i should got the artifact, i cant get it now, anyone got any idea? Im on chapter 20 now

Glitch…might have to just replay the mission
If you’ve tried that then unfortunately the playthrough or get into someone’s game that is around that mission and re-do then
Good luck…sorry that happened to ya!

Thats what i thought.