Chrome: serviceWorker.ready() resolves before service worker is active after unregistering

This seems like this issue: https://github.com/w3c/ServiceWorker/issues/1139 but I am wondering why I only see this error on Chrome?

My scenario is this:

I click a button to register which does the following:

navigator.serviceWorker.register('./sw.js', { scope: './' }).then(...)
navigator.serviceWorker.ready.then(registration => {
    registration.pushManager.subscribe...
    ....
}

Then I later click a button to unregister which does the following:

navigator.serviceWorker.getRegistrations().then(registrations => {
    for (let registration of registrations) {
        registeration.unregister()
    }
})

Then, I re-click the button to register. But this time the the .ready() resolves before the .register() resolves leading to an error when subscribing for push (no active service worker). No matter how many times I click the button register, I keep getting the Subscription error even though the first time it activates the service worker...

When I tried this same scenario on Firefox, it worked as expected. If it is a bug on Chrome, is there any workaround I could do to wait until the registration is ready before subscribing?

EDIT: It seems like Firefox the behaviour is similar on firefox, but for some reason on Firefox the pushManager subscription is able to see the active service worker, but not on chrome.

Start by reproducing the unregister and re-register sequence using navigator.serviceWorker.register, ready, getRegistrations, unregister, and pushManager.subscribe. Compare the observed behavior with the linked W3C issue and the Firefox result; done would require a confirmed explanation, specification change, or documented workaround.