Traffic targets showing altitude of 0

This was my third flight with the FlightBox coupled to ForeFlight on my iPad mini. On the two previous flights the traffic displays were normal. On this flight many traffic targets were displayed but all were showing an altitude of 0. Any ideas?

This is a known issue with ForeFlight. Typically it is brought on by an interruption in GPS signal, then ForeFlight starts showing all relative altitudes as “0”. To “reset” ForeFlight, double tap the home button and swipe UP to close the app, then re-open it.

Thank you. Turns out I had to re-boot my iPad too. Now it’s working 4.0.