Hi @LeahW - My apologies for the delay in responding to you. Thank you for that information and for providing those images for reference. I’ll add them to my report for the team!
Regarding updates, the team are working on one but I don’t have details on when it’ll be released just yet. Rest assured when it is released there’ll be an announcement on the forums for it 
Thank you for the update.
We’ve narrowed the major issues with P2 not being able to see items in crates down to them being items added by P1. We can usually both save, back out, and rejoin and it is fixed. Sometimes if I am booted out for whatever reason, we have a hard time getting it to resync when I join back up.
One of two things typically happen with the crates. Either P2 tries to open the crate to see the items, and a full size version of the items extends out of the crate but is untouchable, and the items in the crate are not visible…
Or the crate opens for P2, the items inside are not visible, but a large item does not extend out. If P2 then tries to put items in the crate, the number of items that can be held in the empty spaces will go into the crates. It will allow them to continue adding items equivalent to the number of items they are unable to see, but the items “overlap” and visibly drop onto the ground in front of them. The items that are on the ground cannot be touched or picked up, but if the player opens the crate and removes the items they inserted, the ghost items on the floor in front of them usually disappear.
We have also found a trial and error that we tend to have fewer issues when P2 issues the sleep command at the end of the day and saves immediately after waking, every day. The longer we play coop in a day, the more buggy and out of sync it tends to get, even with shutting down and reinitiating the session periodically.
Hopefully this info helps the devs narrow down some triggers.
Hi LeahW - Thank you so much for detailing your findings with this issue, I shall add your comment to my report so the team can reference it when testing.
Thank you again!
If you are having the multiplayer empty crate issue talked about above, I have found a fix. P1 must go to every crate that shows no items/empty for P2 and pick up all the items. Place them back into the container and P2 will be able to see them again and interact with future containers. We have been having P2 save and sleep as suggested above as well. Hope this helps!