NF18ACV 5ghz Wifi crashes under load?

Hiya, we've just got slingshot UFB installed and are currently using the default NF18ACV as a wifi router atm. Under load it seems to crash the 5ghz wifi when i transfer files over the network via the 5g, i.e Computer to computer, not over the internet. (While yes this isnt ideal, its handy for transfering movies to my laptop etc.) It will cap out the Upload/download for a minute or two then suddenly the 5g will just lose internet access as well as network access( i.e cant even connect to router itself while connected.), If you disconnect from it you cannot reconnect to the 5g until a complete reboot of the router. 2.4 works perfectly fine during this btw.

Has anyone had experiance with this, or any ideas that might help? Our old router always handled this fine (netgear D7000) but we need the homeline POts from the NF18ACV (because Slingshot do their Homeline via the RGW), and ideally dont wanna add another router to our setup.

Router is running all default settings that were assigned when we received it

Manufacturer:

NetComm Wireless

Product Class:

NF18ACV

Serial Number:

181122510059

Build Timestamp:

180718_1140

Software Version:

NF18ACV.NC.Vocus-R6B038.EN

Bootloader (CFE) Version:

1.0.38-118.8

DSL PHY and Driver Version:

A2pv6F039v.d26r

VDSL PROFILE:

No profile

Wireless Driver Version:

7.35.260.64013

Voice Service Version:

Voice

Uptime:

0D 4H 7M 9S

On a side note: the router/ONT is in the corner of our house -Plus this seem to be the catalyst for an upgrade -so have been considering running a line to set up a AP in the middle of the house(its 7mx15m house so pretty small), probably a Grandstream GWN7610, and using the NF18ACV as just a router and disabling the wifi functionality. Would this be overkill, or a better alternative?

Cheers