might not be the right place for this, if so I'm sorry.
I was having a bit of an issue with the new version of the previewer 2.31 under wine/ubunutu/linux/gnu/etc/etc.
program would load fine, convert to mobi, but would crash on trying load either the resulting mobi from the internal kindlegen or mobi from another source (cmd line kindlegen, etc), generating a JVM exception in terminal/logs.
after some digging around, I deleted this file:
as instructed by this winehq bug thread:
and that fixed the problem. Hope this helps someone in need!