I've not dislodged my dip tube, but my first time using my FB, I added a short length of tubing underneath to get closer to the bottom of the mash tun. It worked fantastically when I tested with water - only about a cup of liquid left in the cooler.
Not sure if I stirred too vigorously or what during the mash, but I clearly didn't leave enough clearance at the bottom of that pickup tube, and it clogged almost immediately. I had to dump to a kettle, fix the FB, then dump back and try to sparge. Happily my efficiency was still around 70%. I almost went back to my bazooka screen after that, but my next go round went much better.
This doesn't sound like your inaugural usage of the FB though. You've used it with better success previously?