In v4.0.0-beta there is no .dropdown-menu-right class.
It was included in v4.0.0-alpha6 and its there in docs.
That's right because Dropdown now depend on Popper.js and when you applied .dropdown-menu-right to your Dropdown it will be positionned by Popper.js not by CSS
Same here. The menu opens out of page in my right aligned navbar :-(

We cannot help you without a live example in a JSBin or Codepen
I've copied the example dropdown from getbootstrap.com and now it works for me.

Unfortunately i can't reproduce the error.
Closing out then. Please make sure y'all are using the latest code from the new beta docs <3.
I am having the same problem. I have reproduced it here:
I could not reproduce it: https://www.codeply.com/go/ULpwrXl7R1
But in my project i have also this issue since upgrading from alpha.6 to beta:

Can't find the difference
Update:
.dropdown-menu-right {
right: 0;
left: auto;
}
Inserting this into my .css fixed this issue for me.
See my answer here : https://github.com/twbs/bootstrap/issues/23479#issuecomment-323020849
@JavanXD
Most helpful comment
I could not reproduce it: https://www.codeply.com/go/ULpwrXl7R1

But in my project i have also this issue since upgrading from alpha.6 to beta:
Can't find the difference
Update:
.dropdown-menu-right { right: 0; left: auto; }Inserting this into my .css fixed this issue for me.