This has been happening for a few weeks:
POS is listing orders as unfulfilled: randomly. They arrive on the back end as unfulfilled orders when indeed they were fulfilled in store at POS.
There also seems to be a bug with order notifications - Shopify POS is randomly sending shipment confirmation emails. They made a purchase in store and took the items with them - nothing was shipped.
The last update I received was May 31...
After looking in to this issue some more there is a workaround for removing the fulfilled orders from the Orders to Fulfil section of the Mobile app.
If you pull down to refresh on the Orders tab a few times then the fulfilled orders will disappear.
Our developers are still looking in to this and working on a fix and we will reach out as soon as we have an update for you.
After Shopify Unite, I was told they'd be allocating a lot more resources towards POS development and support. I haven't seen any change yet. Like I've said in other threads, I'm really just hoping they don't drop POS altogether and leave us with our pants down.
To anyone at Shopify who is reading: this bug still hasn't been fixed. The "workaround" from above doesn't work after 25 refreshes. That seemed like plenty but I gave up after that.