Those hygrometers are probably +/- 5%, so they might be about right.
1 8g pack in a quart jar can probably do it, but try 2 and see if it's more consistent.
You have boveda, so it should be ~60%, and your probes are within their +/- error for that to be true. The Integra Boost brand are the ones to avoid.. they look like a great price but they suck donkey balls.