Hello Jed.
Sorry but I could not answer you before.
In the end I managed to fix the tiddlers by editing them one by one, since for some reason importing many of them makes them an application tiddler, when in the originals it does not have this indication. And the original tiddlers don't have fields either ...
It happens to me in windows and Linux and I have tried Bob's versions: 13, 15 and test version 16, in all of them the same thing happens to me when I try to import a .json file or when I try to create a wiki in Bob from a Single file tiddlywiki.
At first I thought it was a Tiddlywiki problem, and decided to try a single file version. That way tiddlers are imported correctly without problems.
What I have found is that if I pass a tiddler from one Bob wiki to another Bob wiki, dragging it, I don't have the problem of importing with errors, I don't know why but this way it works ...
Regards.