Chrome has made some changes recently, which causes Flash to not run automatically. Salesforce uses Flash to show preview, so if Flash is not enabled for the Simpplr URL, file previews will not appear automatically.
From Chrome, please go to:
In the "Allow" section, click "Add" and add the first part of url your Simpplr is on. Please put in the first part of url, from https to .com . It should look something like:
Then, please go to the file detail page and refresh. The file preview should now appear.