Using multiple webviews is a red flag for me.
If you're loading content from a remote source (over the web) then the amount of memory used to render that content. Reclaiming that memory can also be a challenge.
I'd start by avoiding using multiple webviews and just create one that you reuse across multiple pages as necessary. (You may need to remove and reassign the parent or create at a "shell" level depending on the structure of your app.)
If you need multiple webviews on a single XAML page I'd also see if you can change things to avoid that if possible.
Of course, first use the built-in diagnostic tools to determine if this is where you should be looking https://learn.microsoft.com/en-us/visualstudio/profiling/profiling-feature-tour?view=vs-2019