RUTX11 no wifi 2.4 when set to 2.4 wifi WAN

After a Factory Restore (I have no cables or SIMs in use) I setup the following…
NETWORK > WIRELESS > SSIDs, scan 5GHz and select my router, add password and named as wifi1,
NETWORK > WAN, set wifi1 as priority…

Everything works great, All laptops and phones can see RUTX11 2.4GHz and 5GHz SSID’s, can connect and can access the internet.

However, as the RUTX11 will be in a van I need the wifi WAN connection to be connected to the house router via a 2.4GHz connection (not the 5GHz as above)

NETWORK > WIRELESS > SSIDs, delete the wifi1 connection setup above.
NETWORK > WIRELESS > SSIDs, scan the 2.4GHz and select my router, add password and named as wifi1,
NETWORK > WAN, set wifi1 as priority.

But now the RUTX11 will not broadcast the 2.4GHz SSID and I have instruments in the van that will only connect on that frequency.
The 5GHz SSID works fine.
I have changed channels, increased power from 70% to 100%, tried different passwords and SSID names but nothing works. The RUTX11 will only broadcast the 5GHz SSID !
Checked with multiple laptops and phones.

Home router is an Asus ROG AX11000, and RUTX11 is on firmware 7.09


can you advise please?