There definitely was a problem in my root region, Dankoville 1, yesterday but I fixed that - whatever it was and whatever caused it - by loading a recent OAR of the region. It reset whatever was causing problems within the region. All of the other regions had been working properly.
But after this fix, it appeared there was still an HG problem. However, after extensive testing today, I can find no problem with HG to or from Dankoville - except for Craft World avatars.
I used multiple avatars and multiple viewers to conclude that there was no problem with HG for OSgrid, Metropolis, Neuland and NewWorld Grid.
However, HG for Craft World avatars is still not working. Those avatars were also unable to go from Craft to other grids such as OSgrid and Neuland. So this problem is not related to Dankoville.
End of testing at Dankoville. Trouble Report #1: RESOLVED!