Hi!
Output from Special:EntityData is cached for 31 days. Looking at the code, it seems we are not automatically purging the web caches when an entity is edited - please file a ticket for that. I think we originally decided against it for performance reasons (there are quite a few URLs to purge for every edit), but I suppose we should look into that again.
That would be nice. Right now I'm using cache-defeating URL to fetch data in WDQS because obviously getting 31-day old data is not good. But if data for Special:EntityData URLs would be purged on edit that could allow to simplify that part a bit and maybe also save some performance impact when running multiple WDQS instances.
You can force the cache to be purged by setting action=purge in the request. Note that this will purge all serializations of the entity, not just the one requested.
That also what would happen on edit, I assume.