A variable is returning NaN even though it's supposed to be a Number

module.exports = {
    data: new SlashCommandBuilder()
        .setName('c')
        .setDescription(''),
    async execute(interaction) {

        const data = await schema.findOne({
            User: interaction.user.id
        });

        if (data.True) {
            const currentTime = Date.now();
            const totalTime = Math.floor((currentTime - data.prevTime) / 1000); //in seconds

        console.log(data.prevTime, typeof data.prevTime, currentTime, typeof currentTime, totalTime);
        }
}

module.exports = {
    data: new SlashCommandBuilder()
        .setName('c')
        .setDescription(''),
    async execute(interaction) {

        const data = await schema.findOne({
            User: interaction.user.id
        });

        if (data.True) {
            const currentTime = Date.now();
            const totalTime = Math.floor((currentTime - data.prevTime) / 1000); //in seconds

        console.log(data.prevTime, typeof data.prevTime, currentTime, typeof currentTime, totalTime);
        }
}