V3ra
I got stuck in Tesco's so-called queue too on Friday morning, despite signing in at 6.45 am. My DiL, same region, signed in at 7 am., got into the site almost immediately and booked a slot very quickly for the 23rd, the day I had hoped for.
When I was still waiting at 8.30, DiL took my details and she and DS both signed into my account from their devices - one of them got onto the site and booked me a slot within five minutes (for 21st, not the day I had wanted, but it was the only one left by then, and far better than nothing), while I was still stuck in the wretched queue!
I looked on Tesco's Facebook page later, and it seemed that a lot of people had a similar experience - no luck on one device, but got in via another!
Tesco's only advice to those who failed to get a slot because of this problem was to try again this coming Friday, or keep checking in case any random slots become available through cancellations.