System Information
Operating system: Windows 10 Pro
Graphics card: GTX 970M

Blender Version
Broken: 2.80 Beta, c97c76c01c1d, blender2.7, 2019-01-04 00:26, as found on the splash screen

Short description of error
Painting in texture paint mode is lagging until switching to Cycles Rendered to Cycles Solid.

Exact steps for others to reproduce the error

• Start Blender with default settings (Eevee)
• Switch to Texture Paint workspace
• Switch to Texture Paint interaction mode with default cube selected
• Create a new Base Color texture
• Paint a stroke on the cube: lagging occurs
• Switch from Eevee to Cycles
• Switch from Solid to Rendered display mode and back to Solid
• Paint a stroke on the cube: no more lagging!