I am using a J-head Hot end, they are wonderfully made but one feature on it seems to be a problem on the rostock. Where the filament is extruded there is a small lip or ridge. This can get caught on any over extruded plastic which is catastrophic for the rostock floating head. So I filed it back to a smooth curved tip instead. It seems to have worked. I also added springs under the headed bed so that in a crunch it could move down out of the way if it really needs to.
Here is a 1.5 hour print job completed. Previously 3 attempts at this failed at one point or another