We are sometimes unable to reuse a SuspendedPage's process for a navigation without destroying that SuspendedPage. This is because the SuspendedPage's process already has a suspended WebPage with a pageID that may be the same as the page that is getting navigated. We currently do not support having more than one WebPage with a given pageID in a single WebProcess. We should try and get rid of this limitation for PSON performance.
We may want to regenerate the WebPageProxy's pageID when we process swap? Will see if this would be feasible. We could also store the original pageID in the SuspendedPageProxy for when we need to reattach to a specific WebPage in the WebProcess.