Mix test --cover crashes with a FunctionClauseError

Hi,

in a project I am maintaining I am working on increasing test coverage. But when I wanted to check the current state of coverage with mix test --cover, I got this error:

Cover compiling modules ...
** (exit) an exception was raised:
    ** (FunctionClauseError) no function clause matching in :cover."-patch_code1/2-lc$^0/1-1-"/1
        cover.erl:2181: :cover."-patch_code1/2-lc$^0/1-1-"(2)
        cover.erl:2181: :cover.patch_code1/2
        cover.erl:2183: :cover."-patch_code1/2-lc$^1/1-0-"/2
        cover.erl:2183: :cover."-patch_code1/2-lc$^1/1-0-"/2
        cover.erl:2191: :cover.patch_code_tuple/5
        cover.erl:2183: :cover."-patch_code1/2-lc$^1/1-0-"/2
        cover.erl:2183: :cover."-patch_code1/2-lc$^1/1-0-"/2
        cover.erl:1649: :cover.transform/4
    cover.erl:602: :cover.call/1
    (mix 1.11.3) lib/mix/tasks/test.coverage.ex:142: anonymous fn/2 in Mix.Tasks.Test.Coverage.cover_compile/1
    (elixir 1.11.3) lib/enum.ex:2193: Enum."-reduce/3-lists^foldl/2-0-"/3
    (mix 1.11.3) lib/mix/tasks/test.coverage.ex:141: Mix.Tasks.Test.Coverage.cover_compile/1
    (mix 1.11.3) lib/mix/tasks/test.coverage.ex:122: Mix.Tasks.Test.Coverage.start/2
    (mix 1.11.3) lib/mix/tasks/test.ex:336: Mix.Tasks.Test.do_run/3
    (mix 1.11.3) lib/mix/task.ex:394: Mix.Task.run_task/3
    (mix 1.11.3) lib/mix/task.ex:439: Mix.Task.run_alias/5

08:53:12.591 [error] Process #PID<0.3787.0> raised an exception
** (FunctionClauseError) no function clause matching in :cover."-patch_code1/2-lc$^0/1-1-"/1
    cover.erl:2181: :cover."-patch_code1/2-lc$^0/1-1-"(2)
    cover.erl:2181: :cover.patch_code1/2
    cover.erl:2183: :cover."-patch_code1/2-lc$^1/1-0-"/2
    cover.erl:2183: :cover."-patch_code1/2-lc$^1/1-0-"/2
    cover.erl:2191: :cover.patch_code_tuple/5
    cover.erl:2183: :cover."-patch_code1/2-lc$^1/1-0-"/2
    cover.erl:2183: :cover."-patch_code1/2-lc$^1/1-0-"/2
    cover.erl:1649: :cover.transform/4

Am I doing something wrong?

Best regards,
CK