Same issue there. I recently set-up a new ipad pro 9.7, upgraded to IOS 11.2.1, set-up as a new device (not from a back-up). 333 photos (out of +4000) are missing in the photo library, displayed as blank thumbnails.
When I press the thumbnail, the actual picture is displayed in full size, I can zoom and even appreciate the live effect but can't edit them. Sharing is also impossible, resulting in an error message. Oddly, on the sharing panel, I can see the thumbnail and also the one for all missing photos ...
When returning back to the "all photos" view, the thumbnail appears very shorthly and .... vanishes.
Problem occurs on every photos in a specific time frame : from september 29 to the iPad set-up date (January, 2). All photos taken before and after these dates are ok. Even in this timeframe, Videos seems ok (a few missing) and all photos coming from other source than the iPhone photo App are ok (whatsapp, scanner pro, others apps). But all photos taken with the iPhone photo app are missing, without any exception.
I have another iPad (iPad Air, same iOs version) and also a Mac and everything is ok on them ! No problem at all.
I've gone through many posts on this same issue, tried nearly everything (except restoring the iPad) like stopping iCloud syncing and reactivate, updating photos on the iPhone or the MAc to force pushing a new version (in this specific case, oddly, when pressing the blank thumbnail I can see the last updates but the thumbnail remains blank, and no edit possible ...).
Very annoying. And also disapointing the fact there is apparently no real support from Apple teams on this topic. If somebody got the issue fixed I'm interested ....