I have learned recently, while doing a walk-through with a couple of players on a team with one story I wrote.
The game crashed while I was playing, and I was separated from the team. I ended up back at the first map of the game. I learned that to catch up with the others, I just had to advance to that map in the story.
I have since place respawn points on all my maps as a standard operating procedure in case people are knocked out of the game, they can get back to the map they were knocked out from.
This isn't something that's specific to the Foundry I think. I've had it happen where I get knocked out of a mission due to a disconnect, but my friend is on the 3rd map or so. Then I have to proceed to catch up by running through motions on those maps to get the next map transition to trigger.
I find that all Foundry missions - even those with respawn points - have this glitch. If you drop out and then go back in, you go to an empty first map, and have to go through all maps to the point you were at when you dropped out. It's most annoying.