diff --git a/apps/transport/test/build_test.exs b/apps/transport/test/build_test.exs
index 2e4d57522a..3786223d38 100644
--- a/apps/transport/test/build_test.exs
+++ b/apps/transport/test/build_test.exs
@@ -33,6 +33,19 @@ defmodule TransportWeb.BuildTest do
     {:ok, %{out: "hello\n"}} = Rambo.run("echo", ["hello"])
   end
 
+  test "rambo remains on hex version (not the ARM-compatible fork)" do
+    # NOTE: on ARM architecture (e.g. Mac M1 etc), a local commit can alter `mix.lock`,
+    # and we want to detect cases where this happens. See:
+    # https://github.com/etalab/transport-site/issues/3820
+    # The test has to take the git-stored version of `mix.lock` and assert on its content,
+    # because the CI doesn't run ARM and `mix deps.get` will overwrite `mix.lock` at the moment
+    {output, 0} = System.cmd("git", ["show", "HEAD:../../mix.lock"])
+    {%{rambo: rambo}, []} = output |> Code.eval_string()
+    # if this test fails, it may be because someone with a Mac M1 unintentionally committed `mix.lock` change
+    # related to a Rambo-tweak, see https://github.com/etalab/transport-site/blob/61eabf185e71b7670e5d750048714636f85c5e58/apps/transport/mix.exs#L99-L111
+    assert rambo |> elem(0) == :hex
+  end
+
   test "make sure Elixir version is same for asdf & CI" do
     assert System.version() == asdf_elixir_version()
   end
diff --git a/apps/transport/test/transport/gtfs_data_test.exs b/apps/transport/test/transport/gtfs_data_test.exs
index 6c74934ebf..82411c218f 100644
--- a/apps/transport/test/transport/gtfs_data_test.exs
+++ b/apps/transport/test/transport/gtfs_data_test.exs
@@ -43,7 +43,6 @@ defmodule Transport.GTFSDataTest do
     {data_import, resource, dataset}
   end
 
-  @tag :focus
   test "build_detailed for map" do
     {data_import, _resource, _dataset} = insert_gtfs_stops([{2.5, 48.5}])
 
@@ -65,7 +64,6 @@ defmodule Transport.GTFSDataTest do
            }
   end
 
-  @tag :focus
   test "build_detailed for API" do
     {data_import, resource, dataset} = insert_gtfs_stops([{2.5, 48.5}])
 
diff --git a/mix.lock b/mix.lock
index 2a5082b786..ced627d17f 100644
--- a/mix.lock
+++ b/mix.lock
@@ -130,7 +130,7 @@
   "tesla": {:hex, :tesla, "1.11.2", "24707ac48b52f72f88fc05d242b1c59a85d1ee6f16f19c312d7d3419665c9cd5", [:mix], [{:castore, "~> 0.1 or ~> 1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:exjsx, ">= 3.0.0", [hex: :exjsx, repo: "hexpm", optional: true]}, {:finch, "~> 0.13", [hex: :finch, repo: "hexpm", optional: true]}, {:fuse, "~> 2.4", [hex: :fuse, repo: "hexpm", optional: true]}, {:gun, ">= 1.0.0", [hex: :gun, repo: "hexpm", optional: true]}, {:hackney, "~> 1.6", [hex: :hackney, repo: "hexpm", optional: true]}, {:ibrowse, "4.4.2", [hex: :ibrowse, repo: "hexpm", optional: true]}, {:jason, ">= 1.0.0", [hex: :jason, repo: "hexpm", optional: true]}, {:mime, "~> 1.0 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:mint, "~> 1.0", [hex: :mint, repo: "hexpm", optional: true]}, {:msgpax, "~> 2.3", [hex: :msgpax, repo: "hexpm", optional: true]}, {:poison, ">= 1.0.0", [hex: :poison, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: true]}], "hexpm", "c549cd03aec6a7196a641689dd378b799e635eb393f689b4bd756f750c7a4014"},
   "timex": {:hex, :timex, "3.7.11", "bb95cb4eb1d06e27346325de506bcc6c30f9c6dea40d1ebe390b262fad1862d1", [:mix], [{:combine, "~> 0.10", [hex: :combine, repo: "hexpm", optional: false]}, {:gettext, "~> 0.20", [hex: :gettext, repo: "hexpm", optional: false]}, {:tzdata, "~> 1.1", [hex: :tzdata, repo: "hexpm", optional: false]}], "hexpm", "8b9024f7efbabaf9bd7aa04f65cf8dcd7c9818ca5737677c7b76acbc6a94d1aa"},
   "typed_ecto_schema": {:hex, :typed_ecto_schema, "0.4.1", "a373ca6f693f4de84cde474a67467a9cb9051a8a7f3f615f1e23dc74b75237fa", [:mix], [{:ecto, "~> 3.5", [hex: :ecto, repo: "hexpm", optional: false]}], "hexpm", "85c6962f79d35bf543dd5659c6adc340fd2480cacc6f25d2cc2933ea6e8fcb3b"},
-  "tzdata": {:hex, :tzdata, "1.1.1", "20c8043476dfda8504952d00adac41c6eda23912278add38edc140ae0c5bcc46", [:mix], [{:hackney, "~> 1.17", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm", "a69cec8352eafcd2e198dea28a34113b60fdc6cb57eb5ad65c10292a6ba89787"},
+  "tzdata": {:hex, :tzdata, "1.1.2", "45e5f1fcf8729525ec27c65e163be5b3d247ab1702581a94674e008413eef50b", [:mix], [{:hackney, "~> 1.17", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm", "cec7b286e608371602318c414f344941d5eb0375e14cfdab605cca2fe66cba8b"},
   "unicode_util_compat": {:hex, :unicode_util_compat, "0.7.0", "bc84380c9ab48177092f43ac89e4dfa2c6d62b40b8bd132b1059ecc7232f9a78", [:rebar3], [], "hexpm", "25eee6d67df61960cf6a794239566599b09e17e668d3700247bc498638152521"},
   "unidecode": {:hex, :unidecode, "1.0.1", "d653e7e9777b7c1bcf48b923bbbb9167ecd21a2a90aabb5a3c65b32c6a359497", [:mix], [], "hexpm", "73b490342603a5b1083e0f8f8b9e9bee4149ada327d1b9cdbaf8259f04699611"},
   "unsafe": {:hex, :unsafe, "1.0.2", "23c6be12f6c1605364801f4b47007c0c159497d0446ad378b5cf05f1855c0581", [:mix], [], "hexpm", "b485231683c3ab01a9cd44cb4a79f152c6f3bb87358439c6f68791b85c2df675"},