Hi guys!
I am having the same issue here in Croatia. I have tried everything: from uninstalling the Facebook App to resetting the network settings, from uploading pics when connected to a HotSpot generated by my HTC (it works) to changing every possible setting. Apart from the HTC-generated HotSpot, none of them worked. I even tried to change my SIM card to see if it was a carrier-problem but NO; even with a different carrier, it still wouldn't work. Last time I got my photos uploaded via data network (3G/4G) was on the 16th of April (Saturday) and it worked like it should be. Two days later (the week after), I was unable to share photos from my Camera Roll with the integrated Facebook option via data network. I tried to upload 5 photos via data network but none of them got online. As soon as my iPhone 6 got connected to a WiFi network, it uploaded all 5 photos instantly. It looks like it keeps them in a queue. My last try would be a hard reset but I am waiting for that.
I have not contacted Facebook yet. This is the first time I see people have the same problem as me since the 16th of April. I thought I was alone! Let's keep in touch and try to solve this. It is driving me nuts!
Device: Apple iPhone 6 64GB
Country: Croatia
Carrier: HT HR (but also tried with VIP carrier)
iOS version: 9.3.1
Facebook version: 54.0
Messenger version: 68.0