A slow loading Visual Overview can be caused by a lot of things. There isn't really a go-to way of solving this, but i typically check the following things:
- Is the UI freezing up during the loading? This can be caused by doing a lot of work on the UI thread (having too many shapes on the Visual Overview) or when a server message is sent on the UI thread (this is harder to spot, but can be investigated with the client test tool or the logging in Cube).
- Is a lot of data being fetched by shapes on the Visual Overview? Typically we're looking for big tables that are used for advanced Visual Overview features (e.g. dynamic positioning, children shapes, ...).
- Are we sure it's the Visual Overview causing the problem? Cards often open on the Visual Overview page. A common misconception is that the Visual Overview is causing the delay when in reality it's something card related. This can be checked by inserting a blank page as the first Visual Overview page. Visual Overview pages are lazy loaded, meaning the load will only start when opening that specific page. See if the delay still occurs when opening the second page of the Visual Overview.
- If none of the previous suggestions work, you can always try removing shapes from the Visual Overview until the Visual Overview is loading quickly again. Typically, it's only one shape that's causing the delay, identifying that shape is crucial into resolving the problem. You can quickly create duplicates of a page in Visio. Remove some shapes from the duplicated page and duplicate it again. You are looking for shapes that cause the loading time of a page to drop significantly.