Hello.

Possibly you have too weak server or incorrect hosting settings.

Please check Recommendations block on the dashboard: 

all values must be green

The example of incorrect configuration:

In such cases, I usually suggest the following variants:

1. You can manually try to import demo files: How to manually import Demo data (if you faced with problems in one-click demo import)

2. If after all the manipulations the error is repeated, you can reload the Demo Import page and click the import again. Progress will continue and imports will continue from the moment of the failure.

Hello.

We have encountered this problem on a number of hosting sites, perhaps this is your case.

Try the following method:

1. Go to Import page and click to Import on Main Demo

2. After an error occurs (Error 0), refresh the page

3. Click to Import on Main Demo. Progress will continue and imports will continue from the moment of the failure

4. If the error repeats, just update the page and continue pressing the import until the bar is full.

In the case of an unsuccessful attempt to solve the problem, you can give me access to the site and I'll see how I can help.