How can I fix my iPad's 5GHz Wi-Fi connection issues?

Just bought a brand new iPad.

my WiFi is split between 2.4 and 5 ghz networks.

Everything works fine on 2.4, but when I join the 5ghz, it keeps disconnecting like every 20 secs.

Same network works absolutely fine on my old 9th gen so must be related to the new one.

Any ideas?

[Re-Titled by Moderator]

Original Title: iPad 11th gen wi fi issue