In my device (j7 nxt) , when sim1 is 4g and sim2 is 3g , then i can not connect to internet via sim2 in 3g connection. when i change the data connection to sim2 it change to 4g sim1 goes to 3g. There should have a option to turn on mobile data connec...
why u r using uc . its not too good, actually its a bad browser. my suggestion is u can go with chrome or opera or mozila firefox.from my site uc is vry bad , for your question uc was just showed that thing for their profits, that's all.