At the moment eZ Platform requires Stash Bundle 0.5, however 0.6 is latests and is the one activly maintained.
Update Flysystem to 1.0.x
Cluster with php7 fails when creating images
Stash cache not persisted after update to v0.6
Tested with sanity tests on master on single and cluster installations
Merged in https://github.com/ezsystems/ezpublish-kernel/commit/5e7c1b162b9c898060ddd2f760547eb2bc2f2352