Thank you for the investigation.
Despite this error, for which I don’t know yet how to locate the invalid products (I searched for plugins to check for invalid WC products, but with no luck), my Mailchip.com account seems to continue receiving new/fresh data from the website.
It’s just that the sync previously seemed stuck at the Orders. Now it is stuck at the Subscribers and I can’t see any progress at all for “Subscribers” or “Transactional” or “Unsubscribed”. There are three loading dots instead.
All the rest data of the first column (Coupons, Products, Orders) have been synced. Would that happen if the aforementioned error had any impact on the syncing operation?
Also, is the sync ever supposed to stop? Sync status has been “Running…” for days.