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You can change the target version in the "Edit" page (where you set up all your parameters). The default container is "diginc/pi-hole:latest" (I think—I am not looking at the unraid screen right now—but the ':latest' part is the tag we want to change). To find the available tags, you go to the docker bug page for the container. That's in an earlier post in this thread, and can be found off the Community Applications listing for any given container. In this case, it is https://hub.docker.com/r/diginc/pi-hole/.
So, go to that page and click the "Tags" nav link at the top. Based on the change dates, I figured out that ':latest' must refer to ':debian_v3.3.1' (or newer) and that the version I was running prior to the last update had to be ':debian_v3.3'.
Last step is to edit the container, change the ':latest' tag to the ':debian_v3.3' tag and click Apply. The container will reinstall based on the older version.
I guess I will follow newer releases and try them every once in while to see if the problem is solved. In the meantime, v3.3 seems to work well enough for me.