Roaming issue with full signal

Hi all,

My iphone 6s had been used for 10 months and just fine, starting from this week, I keep having this roaming(loading icon shown beside 3G icon) issue once every day which all my apps have no data support all of a sudden while the signal strength is full(4/5-dots), my phone will only able to regain roaming after reset by flying mode. Anyone know how to solve or having same case with this? is this just iOS problem?

- seems happen after I updated to iOS 9.3.5

- I am using 3/4G network in Hong Kong

- I have reboot my phone twice and still happen

- thats *****

BR