So there is an issue that I run across using power stroke, not very often, but often enough that it can be an issue, where some edges simply don't apply any of the selected join methods whatsoever.

Here's an example. 

To the left: a regular stroke with no path effects applied, and Miter join. 

To the right: the same stroke with power stroke applied, and Miter join option but as you can see it does not work in one of the points.

And messing around with the nodes or miter length doesn't really change anything...

Is there anything that I can do to prevent this, or could this be an actual bug?

Could be the path is not closed.

i'm pretty sure it is closed...

Please share an example Inkscape svg file that has the issue.

Here.

Thank you. I think it's this bug in a new overcoat.

Here's a possible workaround... putting the bug where it can't be seen:

The issue arises at node #1. Breaking the path and reconnecting it moves node #1, so adding a node makes a place for #1 that won't be seen due to its angle.

I see, thanks for the help! Hopefully this is fixable in the near future.