That's exactly what u did to get a connection in the first place. The ONT refused to connect before I cloned the MAC

Sorry phrased badly, the router is set to check and install new firmware every night, so definitely on the latest version.

I'll try taking a backup of the config tomorrow and see if it works.

Router is set to direct connect via the lan port with dchp. No PPoE.

I have the firewall etc settings on asus turned on

That’s is good. Any ASUS AX router should have no issue with 900 / 900 Mbps and without PPPoE things are easier on the CPU.

If you have any of the Trend Micro or other content inspection features turned on try with them off for a speed test.

Turn off QOS on the router

Post deleted by wiggsc00

Their FAQ suggests you need a bridge device to use your own router

Can I use my own router?
Yes, we provide Bridge Mode* service for free. If you plan to use your own router and require bridge mode, please let us know before installation as this will require a special modem to be installed. Otherwise, you will be charged £60 for the extra engineer visit.

*We are not responsible for any configuration issues or processes for routers that are not provided nor placed by Hey!Broadband when installing a bridge mode. Our team only takes care of installation of the “bridge device” to give customers the possibility to use their own router. We kindly invite our customers to flag any issues with the provider of their router.

also do a speed test via the router - on my asus its hidden under adaptive qos and internet speed .........

The ONT is the "Bridge Device". Previously they were plugging the fibre directly into the router.

It seems they're now installing an ONT by default.

That said, I'm running an AC-86U and have not problems with speed, testing with Ookla's PC based tester.

TBB speed tester shows about 1/3 of the true speed.

I run an ax92u which is a dual core armv8 at 1.8GHz, get 300 down and 600 up on my 300Mbit Zen connection.
The OP has an ax82u which is armv7 Tri-core at 1.5Ghz
Wondering if it might max out the CPU single core likely only for WAN.