Have you tried doing a WPS button factory reset on both the router and node, and using the Asus Router smart phone app to set up the mesh? I've had really good results going that way. Then after the mesh is working, you can use the web admin interface to configure the detailed settings. By the way, this firmware version that you allude to (3.0.0.4.386_48706) has worked faultlessly for me.
Here's a reference on what to look for with the WPS button reset:
And yes, if your wifi passphrase isn't 32 characters or longer, you shouldn't need the Beta release...although it wouldn't hurt to try the Beta as well, since there may be more than just that one fix in it.