Thank you, GaianMind.
I have been tracking all of my North American shipments from the past few days, and I notice a strange pattern with some Canadian parcels. Apart from the initial parcel that was held, some parcels are going through a 'Clearance Event' once they're submitted to customs. Thankfully, Canadian Customs is deciding to then clear the packages, and they're now being delivered as before. (Coincidentally, the same customer whose order is now being held received another package that was opened and investigated, then cleared and processed as usual.)
My guess is they've now figured out what this is, i.e. that it's not something people are ingesting like oregano and other essential oils, and they're deciding to give us (and our customers) a break!
On that initial parcel that was held, they're awaiting word from our customer to declare what she intends to use the oil for (i.e. any plans to ingest it? would be my guess).
None of our US shipments have been affected so far, and that includes parcels containing upwards of ten tolas of oil.
والحمد لله ربّ العالمين