I have a Huawei B618 modem with my Skinny Wireless Broadband plan. It's a few years old now. Today it has started dropping 5g band internet connections via wifi, but not 5g via the laptop connected with an ethernet. The 2.4g band via wifi works fine. Restarting the modem fixes the problem temporarily (for anything from 15mins to 2hrs-ish). It's annoying because the speeds via the 5g band are WAY faster than 2.4g, hence my preference to only connect with 5g. 

Before I contact Skinny and ask about buying a replacement modem, can I just check with the technical brains on this forum that this does sound like a modem defect as I suspect it is, as opposed to the sim or a Spark 4g problem in my area? I'm pretty sure it's not this new laptop, as I can reproduce the issue on all 5 laptops and my phone, and that's including up close to the modem. They all show suddenly show "no internet", then "cannot connect to this network" when an attempt is made to reconnect. They will connect to the 2.4g band network in between failed attempts to connect to the 5g band just fine though. After I reboot the modem, the 2.4g band is offered as an available SSID pretty much immediately. The 5g band can take up to 5 mins to be offered, again this is across all devices except the ethernet connected one (which has internet access immediately the modem has come online). The latter issue of 5g being late to be offered in available networks  is actually something I started noticing many months ago, but the losing internet altogether via the 5g band is new today. Restarting connecting devices doesn't fix it, nor does waiting and trying later. The modem has to be rebooted for it to connect again. 

We had 3 power cuts last evening here, affecting a most of the suburb I live in. I'm wondering if this nuked something in the modem, as one power cut was accompanied with the lightbulbs flickering momentarily like a power fluctuation, before the power died completely.