I could go into how FTP (File transfer Protocol) works with it breaking files into little pieces (packets) which are sent with Header info (address and other) attached. Those little packets can be sent all around the globe, passing thru many 'hops' (hubs - just black boxes used for routing). When they all reach their destination the pieces are reassembled into a file. If even 1 packed is lost or corrupt no good file is to be found at the destination.
I don't even know if Adobe uses FTP for their sync system. I do know that the files sent from their 'cloud' to Lr CC for Web use HTTP for the down to our computer direction.
1 file gets broken into many pieces to be sent to the Adobe cloud. Immediately that file is broken into another iteration of pieces for each device/pad/laptop/desktop it is syncing with. That's a LOT of pieces just for one file.
Imagine the user who posted here last week complaining about sync issues when he was trying to sync 70000 + files from Lr Classic into the cloud system and back down to his other systems plus into Lr CC and Web on his desktop. That's millions of packets floating around the globe.
POINT - ? Syncing like Adobe is trying to do is a VERY complicated process that will have a fair failure rate for many reasons.
RAW should be fine Molly, what camera manufacturer/file format though, just in case there is a slight bug.
You can check what is in the sync queue by alt-clicking the Cloud icon (Mac at least).
Although it sounds like bandwidth issue as Jao infers.