I managed to migrate ok following a post...
At that site they advised using a cli to import, so I tweaked their suggestion like so:
php bin/console wallabag:import myuser /app/data/uploads/import/All_articles.json --env=prod --importer=v2which I ran in the Wallabag app terminal (seriously, what a genius idea to add that!), after I had uploaded the json file in the File Manager (and what another amazing idea!!). I had tried and tried from within the Wallabag app, but it would just die. No warnings, nothing in the logs. But doing it with the cli revealed that it was choking on an image format that it didn't like, but at least in the cli it finished the import.
@nebulon Not that I could tell, other than there were no error messages in the logs when I tried importing via the app. I could see it was an image problem because of the cli progress.
Oh, and I had o boost both my Wallabag app AND its Redis to 5 or 6GB of ram each to manage 1200 articles. Anything less than 5GB didn't seem to work. Afterwards I've lowered both to under 1GB and it's all good.