Just guessing but it might be solvable by running the linters in its own mix env. Because lintung causes recompiling. If though the printer compiles faster then Phoenix, it doesn’t see anything to recompile as all beam files are newer as their source files when phoenix gets aware of the change of the source. I do assume similar problems with other editors and linters, but I do not use any lint integration for mine (except for compiling errors), nor do I currently do phoenix.

You’'ll probably need to change the source of your plugin to test, to make it run mix credo with MIX_ENV=lint, you’ll also need to provide conf/lint.exs, which can be a copy of conf/dev.exs for the test.