To reproduce the issue, clone the repo then run npm install and npm run dev (or yarn equivalents).
This example includes the raw data representing the state of a document which is being synced via a "source of truth" server.
The localDoc is a document which has just been updated by a local peer (peer1). Crucially, at the same time it is also receiving sync protocol messages from the server to bring it up to date with a second peer (peer2) which has already synced a couple of hundred changes to the server.
The server doc receives a syncMessage from peer1 and applies it. The result is a document which, when saved, throws a error inflating document chunk ops: mismatching heads error when loaded.
Note that the localDoc state has a count of 181, while the server has already been updated to 200. The change which triggers the syncMessage was to increment the count from 180 to 181.