Hi, Gabe.
I have installed the latest beta version and it didn't help: "High Pass" will not apply the stenciled grey overlay; instead it continues to apply, as I noted above, what appears to be a dark overlay.
Note also: my other filters aren't working, either. For example, when I apply a Gaussian blur, I can increase the blur only to about 16% before an opaque white overlay appears over the photo. See attchments.
Please provide an older version of Affinity Photo for us to use until you're able to work out the kinks in 1.9.1. I really, really dislike the competition's business style but will have to resort to using their software to get my projects done if you're unable to provide an earlier version of your software and / or fix these issues within the next day or two.
Thank you.