The page at
http://build.koreader.rocks/download/nightly shows three downloads for Kindle:
koreader-kindle-arm-kindle5...
koreader-kindle-legacy-arm-kindle...
koreader-kindlepw2-arm-kindlepw2...
Which is the version to be used on Kindle Voyage? I used kindle5 and kindlepw2. Both of them work, but show various errors in the crash.log file.