on a whim, I de-installed the new Navionics app, USA & Canada (the failure was first noticed about the time I bought the new app). And now the old East Coast works again. This is quite repeatable: reinstall the USA & Canada and now once again US East coast does not work. De-install, now it works again. It is not the install of the new app that destroys the old. You must run it, and download some chart tiles in the same area. This happens automatically if you zoom to that area. It does not need to be running simultaneous to the old app, merely to have run prior. I have been using the area around Mount Desert Island. I tried the same thing with the old West Coast and have not been able to make it fail in the same way. I have not tried the old Great Lakes.

I would report this to Navionics but they do not seem to have a support contact.