Well, I experimented with the YAF CSS code. It seems, the following setting in themes\Yafmobile\theme.css makes Code blocks look more-or-less adequate to other Quote and Attachment blocks in the same thread:
.yafnet div.code div, .yafnet div.code {
max-width: 65vw;
}
( the original setting was 85vw )
BTW, you can reproduce all layout problems I get on my Android smartphone using the
device emulation in Chrome DevTools on a big pc (hope, you know this tool). It allowed me to reproduce exactly the same layout I see on my Android smartphone on my pc with Windows 10.