Thanks for reaching out in the community. The auto-save feature best functions when you have a good internet connection and will save every few seconds. You can also manually save your work by selecting file in the top left corner and save from the drop down options.
Can you also try opening the document in a Chrome Incognito browsing session? This often improves performance by starting a fresh cookie session and disabling your extensions.
If you have access to the feature, you can also check the revision history to see if the changes are there. Please see this article for information on how you can restore from a previous version.
If you have not yet lost the work and your Lucidchart document continuously shows "saving" it is important that you do not close your document, refresh your browser, or restart your computer until your work is saved. To proceed with your work, you can copy the content of your document onto another Lucidchart document by following the steps in this article.
If the auto-save feature is still not functioning correctly then that could be a document specific issue. If you believe that there is a document specific issue, please fill out this form and include the document URL, steps to reproduce the issue, and screenshots if applicable.