Did you ever get a fix for this problem?
I have a Galaxy S7 Active and it seems to be doing the same thing as your one...
I note this message was posted from "SM-G890A"
SM-G890A is not a VodafoneNZ sold handset. This handset is intended for AT&T in the USA.
Taking from Samsung's website;
2G GSM: GSM850, GSM900, DCS1800, PCS1900;3G UMTS: B1(2100), B2(1900), B5(850);4G LTE FDD : B1(2100), B2(1900), B3(1800), B4(AWS), B5(850), B7(2600), B8(900), B12(700), B17(700), B20(800), B29(700), B30(2300)
This handset does not support all the required Vodafone NZ bands which I will list below
3G U900, U2100
4G L700 (Band 28) L1800 (Band 3) L2600 (Band 7)
Your handset only supports two of our 4G frequencies we have in operation: L18 B3 and L26 B7. Hence if you are in an area where there is only 4G L7 B28 coverage, you will not have 4G reception.
Please note your handset also does not support Vodafone NZ 3G U900 band, hence you will have issues using 3G in some areas as well..