@boyer NiFi 0.x versions use a whole dataflow revision number when applying changes to anywhere on the canvas. In order invoke a change anywhere (does not matter if you working on different components or within different process groups) on the canvas, the user making the change will need the latest revision number. A user may open a component for editing at which time the current revision number is grabbed. At the same time another use in another browser may do the same. Whichever user makes there change and hits apply first will trigger the revision number to increment. When the second user tries to hit apply, you get the error you described because his change request does not have the current revision. But there is good news.... How this works has changed in NiFi 1.x (HDF 2.x) versions. Revisions are no longer tied to the entire dataflow. While two users will still be unable to make changes to the exact same component at the same time, they will be able to edit different components at the same time without running into the above issue. Thanks, Matt ... View more

@boyer In this case, you can set the 'Max Bin Age' property so that after a given amount of time the merging process occurs even if the group size condition is not met. Hope this helps. ... View more