If you are getting network errors (messages like “it could not be saved”) it could be for one of the following reasons:
1- WordPress has a heartbeat API, which pings the server every few seconds to check log in status. This needs overloads the server.
For example, you open the spreadsheet editor and use it for one hour, heartbeat has made about 100 requests to the server in that hour so when you start saving the server is already busy.
You can use the plugin “heartbeat control” to disable it.
2- Maybe you were saving and logged out and logged in again in another tab. This would invalidate the security tokens and you won´t be able to continue saving.
3- You are saving too many posts at once than your server can handle. Go to the settings and reduce the “posts per batch” setting.
4- You have a bad server = cheap server
For example, if you save 4 posts per batch and the server times out, you´ll get an error. The only solution is to save less posts or move to a better server.
Other customers are able to save hundreds of posts at once when they use better servers.
5- You are too far away from the server.
For example, if you are in the United States and you are editing posts for a client from Australia, the saving will take longer because of the distance between you and the server.