UPDATED; Scanners are back on and are now considerably faster.
We are making some changes to the scanners this morning to use a different set of Steam API endpoints.
This is intended to make the scanners both faster and more reliable, but requires a certain amount of remapping of achievements data from the old to the new API.
While I map that data, it's necessary to turn the scanners off. I'll be turning them back on again as soon as the mapping is completed and we'll move over to the new API immediately!
Thanks for your patience during this time.