Ok. 2 things:
1. Were you the host or someone else? If someone else, did they also have the quest on this step?
2. Was the strike ran from the strike playlist or from directly selected on Tangled Shore map?
Ok. Then I’m thinking the most likely reason is not getting enough of the items that create the platforms (as you are missing the final platform & it looks like you only got 3-4 of them).
I’ll try it again and get them all. But I’ve gotten the final chest on my Day 1 console account (this is my New Light PC account) by getting only one of them.