Well that was an amusing faff!
At the desk the folks were very confused that we didn't have an ETA (we are residents, not visitors), but someone recognised the share code thing... so then they got a tablet to check the share codes manually against the Home Office website. Except the first tablet was giving them an error. They got a second tablet and this kinda worked, though it took several goes because the Home Office site itself kept giving a "Service Unavailable" error mid workflow (its like a 4 step workflow). They asked me to verify it was for residency, just verbally like.
They then updated something on their system which clearly included a manual description in French of the process and the resuult... and said the app would refresh and give us a boarding pass... except that also took a few minutes.
This all took about 15 minutes I reckon. Which is not terrible as an individual, but is terrible as a process.