Cannot access a node js require from a parent scope

So here is how my code looks like :

const mod = require("./module.js")
let functionA = () => {
    return new Promise((resolve, reject) => {
         databasequery("sql", (response) => {
             databasequery("sql", (response) => {
                 console.log(mod)
             });
         });
    });
}

When I call this functionA, the console.log() prints {}, like if mod was an empty object. But when I move the mod definition into the scope of the function like this :

let functionA = () => {
    const mod = require("./module.js")
    return new Promise((resolve, reject) => {
         databasequery("sql", (response) => {
             databasequery("sql", (response) => {
                 console.log(mod)
             });
         });
    });
}

Suddenly, my console.log outputs me the expected object, with the functions I exported in my module.

Can anyone explain why changing the scope of the module suddenly makes everything work / break ?

Note : I don't set / create a mod variable ANYWHERE else in the code.

Note 2 : obviously, those aren't the real names of the function and module nor the real content, and my query functions look different too, but I tried to keep the hierarchy of callbacks and promises the same.

Note 3 : this is a cyclic / recursive require, but I don't see why would that be a problem.

Edit 1 : A few functions are exported from the required module. In my module source, the export looks like this :

module.exports = {
    "createInstance": createInstance,
    "getCurrentWebsocket": getCurrentWebsocket
};

Edit 2 : I reported a bug for nodejs https://github.com/nodejs/node/issues

Edit 3 : module.js code :pastebin.com/QxmxDfhm