after receiving my CRS317-1G-16S+ I've just tried it out and upgraded to 7.1beta4 (development) , factory loaded was 6.44.6. No changes in default conf, all ports bridged, only bridge IP have been changed.
I connected with winbox to the device trough RJ45 port and all was working fine. Connecting trough an SFP+ 10G fiber winbox was connecting but all windows were blank (no interfaces, etc...), but changes like new items created were commited.
I've finally discovered that this was due to the Jumbo Frames (4088 byte) activated on the intel SFP+ PCI network card on my PC. Disabling the Jumbo Frames it worked perfectly.
This happens only when connecting to the CRS317-1G-16S+ with V7 beta. Even with Jumbo Frames activated the connection to many other devices including an RB3011 or cAP with 6.48.1 works fine.
I've not stressed the connection in other ways, but the Internet or LAN browsing works even with Jumbo Frames, the issue with Winbox was the one I found immediately.