When Real-Time Thumbnails are enabled in the content browser and you have many blueprints with static meshes (or anything that is rendered in the blueprint's viewport), the real-time tooltips cause heavy framerate drops when the cursor is hovering over the content browser.
Please note that the effect of this framerate drop is heavier with every extra thumbnail that is added. The blueprints in question also need to be loaded at least once, otherwise the thumbnails are not updated in real-time.
This did not occur in 4.13.2-3172292+++UE4+Release-4.13
Workaround: Disable Real-time Thumbnails in the Content Browser's View Options
Head over to the existing Questions & Answers thread and let us know what's up.