One more observation, and a correction to my own assumption. I saw in the Moves thread (post 29) that imported items “arrive locked, and locked items are the ones the timeline processor won’t merge or edit”, so I take it waiting for the old app to process them won’t help.
Looking more closely at the log, the two reads behave differently:
Read 4198 places from ArcApp database (was 2,221 before my restore, so +1,977, roughly all the places I imported)
Read 46586 timeline items from LocoKit database (was 42,114 before, so only +4,472 of the ~45,000 items I imported)
So the places I restored via Arc 3’s File Importer are visible to the migration, but the timeline items mostly aren’t. Does the File Importer write items somewhere the migration’s LocoKit read doesn’t cover, or are imported items excluded from that query (locked, or by source)? If it’s a source/flag thing, is there anything I can do on my side?