UN687095178CN is a tracking number for package sent by using China Post Ordinary Small Packet Plus which is a cheap service of China Post. China Post doesn't provide tracking service for it after it moves for some stations in China. So, you can't get more update after Dec. 18, 2018.
It's easy to be lost as it couldn't be tracked during the whole process. If you couldn't get it within two months, that's not normal. You'd better contact the seller or open a dispute on AliExress to ask for refund or send one again to you.
I haven't received yet my very discrete China Post packet RV360040800CN, the sender of my very discrete China Post packet RV360040800CN is totally unknown, do I correctly understand that China Post and the destination distribution postal center is waiting for some money bribery from me for urgent dispatch of the China Post registered tracked packet RV360040800CN to me?
It's easy to be lost as it couldn't be tracked during the whole process. If you couldn't get it within two months, that's not normal. You'd better contact the seller or open a dispute on AliExress to ask for refund or send one again to you.