Why does my JWT token expire before the expiry time I set?

Problem

I am building an authentication system using JWT in Node.js. I set the token expiry to 1 hour but users are getting logged out way before that.

What I am doing

I am generating the token like this:

const token = jwt.sign(
  { userId: user.id },
  process.env.JWT_SECRET,
  { expiresIn: '1h' }
);

And verifying it like this:

jwt.verify(token, process.env.JWT_SECRET, (err, decoded) => {
  if (err) {
    return res.status(401).json({ message: 'Token expired' });
  }
});

What I expected

Users should stay logged in for 1 hour before the token expires.

What is happening

Users are getting logged out after just a few minutes even though I set expiresIn to 1h.

Questions

1. What could cause a JWT to expire before the time I set?
2. Could server time zones or clock differences between servers cause this?
3. Is there a way to debug what expiry time is actually being set on the token?