Maintenance Page using multiple ifiles

The images cause a new http get request, therefore you do not see them in the response created by the LB_FAILED event.

Either catch the image request and respond separately in HTTP_REQUEST event...

set css xxx-css
set logo xxx-logo
...
switch [HTTP::uri] {
        "/xxx.css" {
            HTTP::respond 200 content [ifile get $css] "Content-Type" "text/css; charset=utf-8"
        }
        "/xxx.png" {
            HTTP::respond 200 content [ifile get $logo] "Content-Type" "image/png"
        }
}

Also try adding Content-Type image/png header. The code works with us (11.5.1 sw). We put the iFile names into variables as they were needed elsewhere in the iRule logic.

... or you do it inline in the LB_FAILED by b64 encoding into response html, something like:

set img [b64encode [ifile get $logo]]
...