It's happening across any file I open. Albeit most of our files are of similar complexity and size - generally 2 to 6 artboards, each containing a web design. This doesn't seem excessive, and has never previously been an issue;
It's vitally important that this is resolved as swiftly as possible. At present XD is literally unworkable - I click on a page element and the application freezes for around 30 seconds. And other applications become unresponsive as XD is constantly pushing the CPU to 100%.
We understand your frustration and yes we did see customer reporting issues with XD 42. There is a latest update available to XD i.e XD 42.1 version. We highly encourage you to please update XD to the latest version which has fixed few of the similar issue.