I'm having the same issues.. I only have three locos, the latest one was fitted with it's decoder today. Yesterday I had absolutely no issues, neither of the locos had little blue "H" and both responded perfectly to commands from my android tablet.. Today I received a new decoder from Hornby, exactly the same as fitted to my existing locos (HM7000-8TXS) I fitted it to my 08 shunter and sat it on the track all alone to do the downloads/updates etc. All went well, everything worked as it should so off I went to put the body back on... returned to the track and put all three locos on to have a play.. that didn't go well. my existing locos connected but the 08 wouldn't, I thought I'd pinched a wire or something but no, all looked good. I tried it on it's own, still would have no of it.. Anyway to cut a long story short.. It would appear that I now have a "Host" loco which can be the 08 if it's on the track alone, If I add another loco (my 55) whilst the 08 is host then the 55 doesn't connect until I restart the app but then the 55 becomes host and the 08 won't connect.... If I then add my 47 it connects straight away. I just cannot get all three to connect at the same time.. very very annoying and puzzling.. Pete