First: Help > Report a Bug... just takes you to the documentation so not sure what that's about.
We've seen that yesterday, the report a bug button disappeared for some reason, we are taking a look at it.
When you change between graphs (double click on them in the Explorer or right click "Display outputs in 3D view") any outputs that are not used in the current graph still show in the 3D view as the old outputs. So say your last graph had an AO output and the graph you just opened dus not, the old graphs AO output is still being displayed on the model in the 3D view...
Ok, we'll try to change this behavior.
After working for a while any copped or duplicated nodes just stop working. They say 0seconds and never update in the 2D view.
This one is very strange.. What kind of node were you manipulating ? Did you make any functions with division by any chance ? Out of curiosity, was the "white noise" involved ?
After getting frustrated I tried exiting Substance Designer and reopening it... well now looks like SD can no longer be reopened after you just closed the program. I had to restart my computer just so I could start SD again.
Sometimes, SD takes some time to actually close (take a look at the task manager).