How did it break? Do you have link? Maybe I will be able to help.

In general the plan is to shift away from Elixir’s Logger formatters and backends and instead make use of Erlang’s logger.

So the “simplest” way for “modern” handling would be to (unfortunately) write custom formatter (that implements one function format/2) and then use it together with whatever backend you like.

EDIT:
I will try to provide an example later.

we use ink at work.
Test with Elixir 1.10:

ex(4)> Logger.add_backend(Ink)     
{:ok, #PID<0.24432.0>}
iex(5)> Logger.remove_backend(:console)
:ok
iex(6)> require Logger
Logger 
iex(7)> Logger.info("test", %{current_user_id: "qweqe"})
{"current_user_id":"qweqe","domain":["elixir"],"erlang_pid":"#PID<0.24423.0>","file":"iex","gl":"#PID<0.65.0>","level":"info","message":"test","time":1580851293206227,"timestamp":"2020-02-04T23:21:33.206Z"}
:ok

Luckily the fix should be easy: just remove the fields with process information from the metadata. It probably already keeps a list of fields to remove, we just need to update it.