Multiple singleton instances across files in TypeScript and NextJs

Recently, I have been working on a personal project involving the creation of some API endpoints using NextJs and TypeScript that call back on the Discord API using discord.js. Please don't get scared off at the mention of the discord API if you have never touched it, I don't think that library is the issue, hence why it is not included in the thread title.

Problem:

I have implemented a singleton for the discord.js API client as the client can take about a second or two to login and initialize, time I don't want to add to each response. This works great on one file/endpoint, where once that file has the instance, it keeps its. However, as soon as I load another file/endpoint, it creates another instance of the singleton, however, after its creation works fine again within that file.

My problem is that I dont want an instance per file, but instead want one instance for the entire application.

DiscordClient.ts:

import { Client } from 'discord.js';

class DiscordClient {
    private static discordClient: DiscordClient;
    public APIClient: Client;

    private constructor() {
        this.APIClient = new Client();
        this.APIClient.login($TOKEN);
    }

    public static get Instance() {
        if (!this.discordClient) {
            this.discordClient = new DiscordClient();
        }
        return this.discordClient;
    }
}

export const DiscordClientInstance = DiscordClient.Instance;

NOTE: token is merely a placeholder for the unique token of my bot application registered with discord.

/pages/api/test1.ts

import { DiscordClientInstance } from "../../DiscordClient";


export default (req, res) => {
    let guild = DiscordClientInstance.APIClient.guilds.fetch($GUILD_1_ID)
        .then(guild => {
            console.log(guild.name);
            res.statusCode = 200;
            res.json({ name: guild.name });
        })
        .catch(console.error);
}

/pages/api/test2.ts

import { DiscordClientInstance } from "../../DiscordClient";


export default (req, res) => {
    let guild = DiscordClientInstance.APIClient.guilds.fetch($GUILD_2_ID)
        .then(guild => {
            console.log(guild.name);
            res.statusCode = 200;
            res.json({ name: guild.name });
        })
        .catch(console.error);
}

NOTE: $GUILD_#_ID is merely a placeholder for where the the id of the discord server I am fetching would go.

As can be seen above, test1.ts and test2.ts are nearly identical and are inheriting the same const.

If anyone had any clues as to why this is happening, I would be very appreciative. Some people on other sites from my late-night googling have suggested this could be an issue with node, however, I honestly have no clue.

Thanks, Matt :)