gitlab parallel:matrix does not run concurrently - gitlab

Question

I am trying to get a job to run in parallel within gitlab. I have registered 8 runners on one server and set concurrent=16 in /etc/gitlab-runner/config.toml. I see all 8 runners configured within that file. Below is the beginning of the file:
concurrent = 16
check_interval = 0
[session_server]
session_timeout = 1800
[[runners]]
name = "gitlab-runner-02-#1"
url = "http://gitlab.example.com"
token = "redacted"
executor = "docker"
[runners.custom_build_dir]
[runners.cache]
[runners.cache.s3]
[runners.cache.gcs]
[runners.cache.azure]
[runners.docker]
tls_verify = false
image = "almalinux:latest"
privileged = false
disable_entrypoint_overwrite = false
oom_kill_disable = false
disable_cache = false
volumes = ["/cache"]
shm_size = 0
[[runners]]
name = "gitlab-runner-02-#2"
url = "http://gitlab.example.com"
token = "redacted"
executor = "docker"
[runners.custom_build_dir]
[runners.cache]
[runners.cache.s3]
[runners.cache.gcs]
[runners.cache.azure]
[runners.docker]
tls_verify = false
image = "almalinux:latest"
privileged = false
disable_entrypoint_overwrite = false
oom_kill_disable = false
disable_cache = false
volumes = ["/cache"]
shm_size = 0
.gitlab-ci.yml:
image: almalinux:latest
stages:
- build
foo:
stage: build
script: sleep 60
parallel:
matrix:
- foo: [a, b, c, d, e, f, g, h]
From everything I've read, this should be enough for it to run in parallel. And yet, all the jobs run sequentially. What am I missing here?
Edit:
I've crossposted on gitlab's forum. I will make sure both gitlab's forum and stackoverflow have the answer clearly listed when I find it. https://forum.gitlab.com/t/parallel-matrix-isnt-executing-in-parallel/72095
Update:
I seem to have resolved the issue. I need to do more experimenting, but it appears to be related to another registered runner on a different server not allowing more than one job. I also increased the limit for each individual runner. I need to do more experimenting to understand what actually fixed it still.