I have noticed it as well. It does the whole "..." thing. I have not looked into how to view the whole message as I had to switch to Textra once I found out the stock messaging app doesn't handle group texts correctly.
Sorry I'm not much help.
EDIT: I just went and looked at a conversation thread from yesterday that was cutting off the message and it now appears to be showing all of it. Quick little tip I found is that you can re-size the message bubbles by doing a pinch to zoom type action while on the actual conversation thread. Hope that helps.