Last night I started having problems sharing files on my fully up-to-date iPad air.
With Christmas and the New year there has been lots of exchanging of photos and movies between the various members of the extended family group both at home and in various parts of the world.
For example I select 2 photos of the grandchildren to send to an auntie in Holland.
Select them, Hit Share, Select Messages, A Messages window opens up ready to be addressed - but the images are not there., just a text box for the message.
I tried several times last night with various photos and a short movie to several different people.
Then this evening, as seems to be the case with all my problems - it’s working perfectly
Assuming you tried rebooting your phone, strange behavior like this is often attributable to being very low on storage on your iPhone, especially for activities that require i/o, like the one you’re doing.
I’ve seen similar, as well as trying to send a dozen photos and it failed to send them, so tried smaller batches, which worked.
When I noticed the lack of photos I tried changing from mobile data to wifi (thinking the photos first needed to be uploaded before being displayed) and if I recall correctly that didn’t help with photos appearing in the Message. YMMV.
Also lately problems with Messages communicating from living room sofa MBA on one logged-in Apple Account to a MBP in the same room, logged in to another Apple Account. Sometimes the Message appears after some hours, sometimes not at all, sometimes logging out and back in helps, sometimes not.
Messages notifications are also not working, on Macs or iPhone. So I try to use Messages only when I have time and patience and the app itself open and in front.
If you didn’t change much and now it’s working again, possibly something in the Intertubes was slowing down the display.