Cannot use 3G/HSDPA network in some conditions

[Reach052]

Hi,

I have a Xperia Z3 Dual (L55u, Mainland China Ver) and I am now using Vodafone in Australia.

I have problem using 3G network in most non-4G areas, where the signal displays normally, but when I try to browse sites or use any app connecting to internet, it lags and display "cannot connect to internet". 

This happens both on its original firmware (L55u_23.0.F.1.78_CN) or RU firmware (D6633_23.0.1.F.0.96_RU). 

4G network works normally.

Does it help if I upgrade my firmware to 23.0.F.1.82? Or will there be a solution to use 3G network normally? Thanks!

[Uliwooly]

Do you have the corect APN settings?

[Reach052]

Yes, I am pretty sure that I used right settings in APN. In fact, I am able to use 3G network occasionally, but not often. However, when I can't access to internet, the 3G signal is normal.

[JakeSully]

could be some APN issues, try going to settings --> More --> Network Settings and see if it fixes it, if issue remains then it could be a issue with Carrier in australia or problems with their towers causing your phone to fail on 3G usage.

[Uliwooly]

How old is the SIM card? 

is it a NANO SIM card or did you trimmed a regular SIM card?

Was this phone locked to another carrier/network branded? 

go to settings > about phone > status > signal strength, what do you see?