The missing one seems to not a widget provided with this add-on. You will need to contact its author unfortunately.
But @RoldanLT figured it out I think, must be a <h3 /> tag missing.
A temporary workaround is apply the max height via CSS? You should find a unique ID for the panes div. Sorry I couldn't get it for you because it looks like the newest thread widget is not showing up for guests (because of permissions?)