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
Merged in https://github.com/ezsystems/ezpublish-kernel/commit/5e7c1b162b9c898060ddd2f760547eb2bc2f2352
Tested with sanity tests on master on single and cluster installations