Group runner very slow to pick up jobs when more than one group

I started with one group and added a group runner.

Initially with one group the runner was very fast to pick up jobs (almost instantanously)

I've since added two more groups, as i understand i can't share runners across groups?

Thus i registered two more runners on my box.

[root@runners ~]# gitlab-runner list
Runtime platform                                    arch=amd64 os=linux pid=1247 revision=8bb608ff version=11.7.0
Listing configured runners                          ConfigFile=/etc/gitlab-runner/config.toml
group1                                              Executor=docker Token=******************** URL=https://gitlab.com/
group2                                              Executor=docker Token=******************** URL=https://gitlab.com/
group3                                              Executor=docker Token=******************** URL=https://gitlab.com/

Since doing this its become very slow to pick up new jobs. The job stays pending for on average for 3 - 5 mins.

gitlab-runner is on a dedicated box and i've made no other config changes AFAIK

my config.toml

concurrent = 1
check_interval = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "group1"
  url = "https://gitlab.com/"
  token = "********************"
  executor = "docker"
  [runners.docker]
    tls_verify = false
    image = "tetraweb/php:7.1"
    privileged = false
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache"]
    shm_size = 0
  [runners.cache]
    [runners.cache.s3]
    [runners.cache.gcs]

[[runners]]
  name = "group2"
  url = "https://gitlab.com/"
  token = "********************"
  executor = "docker"
  [runners.docker]
    tls_verify = false
    image = "tetraweb/php:7.1"
    privileged = false
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache"]
    shm_size = 0
  [runners.cache]
    [runners.cache.s3]
    [runners.cache.gcs]

[[runners]]
  name = "group3"
  url = "https://gitlab.com/"
  token = "********************"
  executor = "docker"
  [runners.docker]
    tls_verify = false
    image = "ruby:2.5.0"
    privileged = false
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache"]
    shm_size = 0
  [runners.cache]
    [runners.cache.s3]
    [runners.cache.gcs]