Item shipped via Royal Mail Registered Mail (UK) to china returned

This is an example item being shipped from the UK via Royal Mail registered air mail and then eventually returned back to the sender. Not knowing what's the reasons usually the recipients side should have the info either their customs or not successfully delivered or the recipients refuse due to some reasons. The tracking information can be tracked on Royal Mail tracking page and china post tracking page. As you can see the time of delivery and eventually it has returned takes a long long time which is very frustrating.

Item:
RU830799325GB
Service
International Signed
Latest update: Delivered
Your item, posted on 09/01/17 with reference RU830799325GB was delivered in GARSTANG PDO on 03/03/17.
Thank you for using our International Signed service.



China Post Register Air Mail Tracking System

Parcel No.RM830387112CN tracking result

2017-05-18 09:38:37.0 中邮沈阳仓 received
2017-05-18 13:28:24.0 中邮沈阳仓 customs scan
2017-05-18 13:29:53.0 leaving 中邮沈阳仓 ，next station 沈阳center
2017-05-18 14:30:45.0 沈阳Transit Station export security scan
2017-05-18 14:37:42.0 沈阳Transit Station export customs scan (domestic transit )
2017-05-21 14:18:51.0 Beijing Transit Station export security scan
2017-05-22 15:05:02.0 Beijing Transit Station export customs cleared
2017-05-22 22:59:00.0 arrive Beijing Airport
2017-05-23 02:54:30.0 leaving Beijing Airport going to next airport/seaport