Chromecast cannot connect to GL-MT300N-V2 router

The router is set up with VPN and I can connect a number of devices to the router and they all work fine.
I can also set up Chromecast on my home router and that all works fine.
My problem is Chromecast will not connect to the GL-MT300N-V2 router? Has anyone had a similar issue and/or a solution?

Can you provide some logs at the time of connection?
You can monitor in the background using the logread -f command

Does chromecast cannot find the wifi or it find the wifi but just failed to connect?

I have a Chromecast and it had a lot of problem when connecting to wifi (not MT300N-V2). But after connect it works ok.