Collections seem to sync correctly when done manually but they seem to be disappearing, perhaps on cron run (both products and collections are set to sync on cron on the dev site where I noticed this).
Update after testing:
Once they are gone, a regular sync doesn't seem to restore them, the "Delete all and reimport" option needs to be selected. Then the collections sync again. Running cron makes them disappear again from the "Shopify Collections" vocabulary and from products that use them.
This seems to be related to an outdated usage of $page_info. I'll make a commit that seems to fix it. It would be good to test with a store that has over 250 collections but it's working in small-scale testing.
Collections seem to sync correctly when done manually but they seem to be disappearing, perhaps on cron run (both products and collections are set to sync on cron on the dev site where I noticed this).
Update after testing:
Once they are gone, a regular sync doesn't seem to restore them, the "Delete all and reimport" option needs to be selected. Then the collections sync again. Running cron makes them disappear again from the "Shopify Collections" vocabulary and from products that use them.