macOS: 15.7.7
BetterTouchTool: 6.568
mh looks like some caching issue, 6.568 is not on any update channel. Probably checking for updates again will resolve it.
extracting the update takes much longer then normal before the error appears
it doesn't. i did a manual update from here then later again update from within the app. still the same in v6575
mhh there have been thousands of updates to these alphas already, not sure why it wouldn’t work for you. Have you already tried to restart your machine?
just did it again and now it updated 
great