I had it in use then when taken off and set on a table for a minute to tend to other matters and returning it asked me for a pin and I was never aware of making one.
Are you sure it wasn't simply suggesting that you set a pin? I remember such a message popping up randomly on my Q3 even though I had been using it already for 6 months, some sort of security enforcement app, and it felt like it was strongly trying to coerce me to comply, but then I realized there was a very inconspicuous option to skip doing so, near the bottom.
I ended up factory resetting it from the site showing my devices then tried to get back on and the pin feature was still there.
If it didn't work, then you haven't actually done a successful factory reset. Or maybe it was actually asking you for the STORE PIN? That's the pin to protect your credit card from unauthorized purchases. Looking at instructions found on Reddit, you can try this:
Log in to https://auth.oculus.com/login/
Now open https://secure.oculus.com/my/pin/
Select "Forgotten your Store PIN and need to reset it?"
Select "REQUEST PIN RESET"
You should get an email with a link to reset your pin. Make sure to check your junk mail if you can't find it.
Good luck.