Slow file upload when ASM is enabled

Hello,

We have a web application where image uploads are painfully slow (x2) when ASM is enabled. Virtual:

ltm virtual /PART/uat-app-vs {
    destination /PART/127.0.0.1:https
    ip-protocol tcp
    mask 255.255.255.255
    partition PART
    persist {
        cookie {
            default yes
        }
    }
    policies {
        /ITSS/asm_auto_l7_policy__uat-app-vs
    }
    pool /ITSS/uat-app-pool
    profiles {
        /ITSS/uat-app-ssl {
            context clientside
        }
        http { }
        no-reject-dos { }
        oneconnect { }
        tcp {
            context clientside
        }
        tcp-lan-optimized {
            context serverside
        }
        websecurity { }
    }
    rules {
        maintenance-unavailable-rule
        clickjack-hsts-rule
        secure-cookie-rule
        /PART/acg-rewrite
        /PART/show-error-page-rule
        rewrite-x-fw-for-rule
    }
    security-log-profiles {
        "Log illegal request and response"
    }
    source 0.0.0.0/0
    source-address-translation {
        type automap
    }
    vlans {
        EXT-11
    }
    vlans-enabled
    vs-index 460
}

ASM has the following URL configuration:

Any ideas why?