Meraki versus Sagemcom for my home devices - I should be able to solve this, but can't!

I'll try to keep this short. I'm a sometime network architect, support engineer. Self-taught, probably undercooked in experience. I work with IP networks on a daily basis and have been for 7+ years. I know enough to be dangerous, but don't ask me to wireshark my way out of this :)

I'm annoyed by this, because I feel like it's solveable and I should have the necessary knowledge to get to the solution, but I can't and it's been troubling me for a couple of weeks.

I have cable internet from the second biggest ISP here in Australia (Optus) with their standard Sagemcom F@ST 5353 Gateway.

I have a Meraki MS220-8 switch and two Meraki MR30H APs.

I have two air conditioning units by an Australian brand (Rinnai) with some Chinese Wi-Fi chipset I forget the name of, running an iOS app call 'AC Freedom'. I've managed to get these paired once, via Meraki Wi-Fi but never again after they randomly dropped again. I've followed all the manufacturer rules (2.4Ghz only - no special characters in the passphrase - no spaces in the SSID) and still no pairing to the app.

I had given up, until I got my two new Wyze cameras yesterday. The pairing system between the cameras and the app is eerily similar to the AirCon pairing process - right down to the screen layout, SMS code confirmation countdown timer and the requirements of the network I listed above. Including the fact that it just won't work on Meraki.

The instructions for the Wyze are aimed squarely at the home user with an ISP router ("you'll have two networks, one appended with a 5G or 5Ghz - make sure you don't connect to this one"). So, on a whim I turned Wi-Fi back on in the ISP Sagemcom router and began the pairing process against the default 2.4Ghz network.

BOOM! All good.

Back to the aircon…..yep, you guessed it. Straight in. No issues.

So, why can't the Merakis handle these devices, even with all the 'rules' being followed? I've run out of things to tweak (well, not strictly true, but I've turned off all bells and whistles and defaulted everything down to the basics).

ISP router out-of-the-box: no issues.

Meraki - basic default config - no dice!

I'm so confused and I'd love to get these devices back on to the Meraki network as I'm going to introduce an MX security appliance soon and would prefer my aircon and cameras to be behind something a bit more solid than a ISP router with no firewall.

Any thoughts or lines of investigation you can suggest?

​

TL:DR - ISP router works for devices but Meraki does not. What on earth could the Meraki be doing to prevent these devices working, that the Sagemcom isn't?