Hello Sanghwa

Thanks for posting in the Lucid Community.

There are a couple of issues that we consistently come up against with slowness. Do you mind reading through and seeing if any of these could be the cause of what you are experiencing? 

- What browser are you using? Lucidchart is optimized for Google Chrome so if you haven't already please try the feature in that browser to see if it resolves the issue.

- Also try opening your document in a Chrome Incognito browsing session. This often improves performance by clearing your cache and cookies and disabling your extensions.

- Would you mind connecting to a different network or disconnecting from your VPN (if applicable) to rule out any connection or security issues?

- Having many page tabs large canvases on each tab and a high number of shapes on each canvas all increase the time it takes to load and update when changes are made. If you are working on a very large document you may consider breaking it into several smaller documents to improve performance.

If in spite of trying all the above the issue persists please file a support request here including the following information:

- The URL of the document(s) affected so that I can take a look.

- A screenshot of any error messages or pop ups that appear.

- A description of any document or other changes that happened leading up to this slowness.

- A screenshot of the associated Javascript Console output after reproducing the issue. You can open your Javascript Console by pressing Ctrl+Shift+J (if your computer is a Windows/Linux) OR Cmd+Opt+J (if your computer is a Mac).

Thank you!