Class method with Implicit Return and String Literal Kills Formatting

[redreceipt]

Tried to get this down as small as I could and show the problem although I'm not sure which part exactly is the issue. It ruins the rest of the file by turning everything "string" color. If the implicit return is on the same line, it works fine.

Requisite minimal reproducible example, formatted as plain text :

class Mapper {
  mapFn = () => 
    this.map((id) => `Id eq ${id}`).map((str) => str);
}

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Optional: concerning jsx.

PLEASE PLEASE PLEASE make sure you have properly
setup and are sourcing this plugin https://github.com/mxw/vim-jsx

WE DO NOT support JSX automatically, you need another plugin to add get this
functionality.

Make sure the bug still exists if you disable all other javascript plugins
except the one noted above, mxw/vim-jsx