I have had this issue on a lot of projects - when you start drawing up a sanitary system say you just drew a long run of pipe sloped at 1%. If I go to put a wye fitting in for a take-off it will automatically connect and be at the same slope and I am able to move it anywhere along with run of pipe with it following that slope having the pipes at both ends stay connected the whole time. But, for some reason after a day or so of working that way, Revit seems to decide it doesn't want to do that anymore. It will same as always put the fitting in properly the first time, but if I move it after that, nothing stays connected. This actually happens a lot with ductwork where it will all stay connected while making adjustments and then same thing - after about a day or so when you move things nothing stays connected anymore.
To me, this seems like I must have accidentally changed a setting somewhere to make it act differently. Has anyone else had a similar issue and if so, is there a fix for it?