After much thinking, I decided to give WeChat update a try and it works! After upgrade to WeChat 6.3.15, it just works. I am not sure any fix in 6.3.15 is related to this or a update just solve the problem.
This is the things I tried.
1. Clear WeChat app cache. -> doesn't work
2. Clear System cache. -> doesn't work
3. Update WeChat to a newer version -> OK.