I’m sorry for the trouble you are having with swimlanes, and am happy to help! Just to make sure that we are on the same page, please review our Swimlanes and Container Shapes video, Creating Swim Lanes article, and Swim Lane Flowchart template from the Lucidchart Help Center, and let me know if you have any questions about the intended functionality or set up of swimlanes.
Please try the document in a Chrome Incognito browsing session. This often improves performance by clearing your cache and cookies and disabling your extensions. Please also try turning off WebGL. This can be done by going to View > Use WebGL and un-selecting this option.
Note: apologies for the delayed response here. Our forum host experienced a bug that impeded our ability to respond publicly. However, we wanted to ensure the resolution provided in our 1:1 email support with you was provided here in order to assist other Community members who have similar questions.