SUMMARY STEPS TO REPRODUCE 1. Open a temp 2. Select a standard brush. 3. Draw OBSERVED RESULT EXPECTED RESULT something more natural like I get with Autodesk Sketchpad. SOFTWARE/OS VERSION: Windows 10 Home Edition, Version 1809, Build 17763.194. ADDITIONAL INFORMATION I actually made it briefly disappear using by going into Radeon control panel and reverting my settings back to letting the programs or games to "specify".
I'm sorry, but this is not a bug report. There's nothing in it that we could actually take action on, and from what you describe, it's a problem specific to your system. See https://docs.krita.org/en/KritaFAQ.html#krita-is-slow for some more information.