Thread:Extension talk:VisualEditor/Visual Editor successfully saves changes but says "Unknown error"?

I have VE in my wiki project linked with Parsoid on Heroku. The data parses successfully according to the logs, and the changes apply successfully after using Visual Editor, which means that it's configured correctly, but each time I press "Save page", VE gives me "Unknown error" and doesn't display the results automatically. However, if I reload the page manually, I see that the changes applied.

I've been searching Google for people with the similar issue but it seems that I'm the only one. What do you think the problem might be? Thank you in advance for any help.