tripper1000:

 

According to GIS.geek, if you are only getting B28 (700MHz) and B8 (900MHz) that would indicate that you are likely seeing the Bombay South tower (or Meremere?), which lacks B3 and B1. Given it's elevation and the lower frequencies, it will cover a large geographical area/lots of people. Combined with 2DM's lesser bandwidth in these bands (12MHz for B28 and 5MHz for B8) and the fact that B8 is still shared with 3G on many towers, it has the very real potential for congestion. 

 

Both those (Bombay South and Meremere) are One NZ MORAN sites which only have L700 (the 900 MHz licence is for U900 only).

If OP is getting L900 then it's more likely to be a proper 2degree site -- e.g. Pokeno. It's possible OP is at a location where they can only just get L700/900 and out of range for L1800/2100.

tripper1000:

 

Next time you see no data, have a play and see if switching to 3G improves it. At my place of work inside a semi-rural concrete building, I find I get much better reliability on 3G (B8, 900MHz) than LTE. (LTE mostly beats it for speed when it works, but often doesn't work at all). While 3G has narrow bandwidth, everyone is allergic to it so you might have the whole band to yourself, working out to better (than zero) speeds. 

 

YMMV, I've had the opposite experience where U900 barely works at all whereas L900 works reliabily from the same site, same phone, etc.

U900 is only 5MHz and will be gone end of year anyway so not a viable solution unfourtently. Could be worth a try I suppose for 2 months.