Yeah, surely they are bugged.
I could talk with the first signal after finding diggersby. But the old man appeared for my after I talked the second sign, before that I just saw the diggersby. Nothing special with the old man not the most North sign.
My friend had no signs available and the old man appeared just after talking with diggersby. Still they have NPCs that I can't see (a chef on the left side of the pokecenter and a diggersby that you can't talk with). Their signals are all covered with Meowth, but I don't. We both entered on my phone for checking it was not a big of my temp files: