The block pruning functionality (activated by returning a RetainHeight from Commit) does not seem to be safe for concurrent use. One example of such a scenario appears to be triggerable when LoadBlock is called on the store.BlockStore, for example this part:

If pruning is in progress (concurrently) then bs.LoadBlockPart can return nil as indicated by its documentation:

But since the nil value is not handled correctly this may result in a panic due to a nil dereference.

There seems to be a bs.mtx, but for some reason it is not locked when accessing state via Load* methods. This can result in the state changing while the Load* method is executing, e.g., in the above example the LoadBlockMeta can succeed while the subsequent LoadBlockPart will return nil as the block/part has since been removed.