Custom 503 error files not loaded

Help!
1

Hello,
I have problems with a new plain config to get custom error pages working. E.g. for 503 error I want to use the error file 503-alt.http but it doesn’t seem to be loaded in haproxy.cfg. It still uses the default 503 error file. Permissions on the 503-alt.http are set correctly.
When I paste the contents of my custom error file into the default 503 error file, the error page is displayed correctly.

Here’s the current haproxy.cfg. Do I have any configuration errors in my config files?

global
        log /dev/log    local0
        log /dev/log    local1 notice
        chroot /var/lib/haproxy
        stats socket /run/haproxy/admin.sock mode 660 level admin
        stats timeout 30s
        user haproxy
        group haproxy
        daemon

        # Default SSL material locations
        ca-base /etc/ssl/certs
        crt-base /etc/ssl/private

        # See: https://ssl-config.mozilla.org/#server=haproxy&server-version=2.0.3&config=intermediate
        ssl-default-bind-ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384
        ssl-default-bind-ciphersuites TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256
        ssl-default-bind-options ssl-min-ver TLSv1.2 no-tls-tickets

defaults
        log     global
        mode    http
        option  httplog
        option  dontlognull
        timeout connect 5000
        timeout client  50000
        timeout server  50000
        errorfile 400 /etc/haproxy/errors/400.http
        errorfile 403 /etc/haproxy/errors/403.http
        errorfile 408 /etc/haproxy/errors/408.http
        errorfile 500 /etc/haproxy/errors/500.http
        errorfile 502 /etc/haproxy/errors/502.http
        errorfile 503 /etc/haproxy/errors/503.http
        errorfile 504 /etc/haproxy/errors/504.http

http-errors pm_default_maintenance
        errorfile 503 /etc/haproxy/errors/503-alt.http

frontend stats
    mode http
    bind *:8404
    stats enable
    stats uri /stats
    stats refresh 10s
    stats admin if LOCALHOST


frontend http_frontend
    bind *:80
    mode http
    acl maintenance_mode nbsrv(testsrv) eq 0
    use_backend maintenance if maintenance_mode
    default_backend testsrv

#frontend https-frontend
#    mode http
#    acl maintenance_mode testsrv eq 0
#    use_backend maintenance if maintenance_mode
#    bind *:443 ssl crt-list /etc/pki/tls/certs/crt-list.txt
#    default_backend testsrv

backend maintenance
    mode http
    errorfiles pm_default_maintenance
    http-response return  status 503  default-errorfiles  if { status 503 }

backend testsrv
    mode http
    balance roundrobin
    server srv1 mac.domain.local:80

Thanks,
jpm