Greetings,

I will try to make a small example, but first I would like to check that this is not a know bug. Which should have been possible to find here…

Elixir 1.15, Mix 1.15.6 (compiled with Erlang/OTP 26), umberella project
MIX_ENV=prod mix release
creates a sys.config with, among others, {logger, [... ,{metadata,[mfa]}]}
Trying to start this release:

=CRASH REPORT==== 1-Nov-2023::10:07:38.785472 ===
  crasher:
    initial call: application_master:init/4
    pid: <0.1827.0>
    registered_name: []
    exception exit: {bad_return,
                     {{'Elixir.Logger.App',start,[normal,[]]},
                      {'EXIT',
                       {badarg,
                        [{maps,from_list,
                          [[mfa]],
                          [{error_info,#{module => erl_stdlib_errors}}]},
                         {'Elixir.Enum',into_map,1,
                          [{file,"lib/enum.ex"},{line,1521}]},
                         {'Elixir.Logger.App',start,2,
                          [{file,"lib/logger/app.ex"},{line,40}]},
                         {application_master,start_it_old,4,
                          [{file,"application_master.erl"},{line,293}]}]}}}}
      in function  application_master:init/4 (application_master.erl, line 142)

MIX_ENV=dev does not have the problem, neither did prod in Elixir 1.14.