I tested on 9.4.8 and couldn't reproduce the issue. But there have been a lot of parser issues that are only seen when running 'b load' as opposed to saving an iRule. For this specific issue, it looks like it's been fixed between 9.4.3 and 9.4.8. It would be good for you to upgrade to fix this and many other issues. In the meantime, can you try this for the sorry HTML:
set ::sorry "This site is temporarily not available. If you would like to validate whether this is planned downtime, please click on the xxxx Logo"
Aaron