I noticed if I filled in any particulars which was missing in the shipping address , then after I pressed "save and ship to this address" , the message to seller will be empty.
And also, if you happen to change the shipping method, the message to seller will be gone too.
The another feedback is when the customer using the short form of their State eg CA instead of California, the autofill function does not recognise it and will not fill that in.
Above are just my findings, not big deal but I think some issues can not be fixed as it is Aliexpress problem.