Massive and sudden frame drops in pre- and post-game

During a match, in the pre-game hero select, and post-game team showcase and highlight reel, I’m getting considerably fewer frames than during the actual game itself. This has also caused issues in Junkensteins Laboratory, as the Mutation menus are also lagging. They return to normal after the match begins, but it is annoying as my old PC never had this issue, but my new one does.