Wasn't able to reproduce the issue on 2 other different systems. One is a Dell laptop with Intel HD 4400 (20.19.15.4531 driver version), and the second is a desktop PC with integrated ATI Radeon HD 3000 graphics (8.970.100.9011 driver version). Both performed as expected either on 1080p60 and 1440p60, 4k60 was not testable due to hardware limits. The only system on which I reproduced had Intel HD 630 with latest driver installed and only on 4k60 (maybe there was a recent update for these gpu's which added an incompatibility and triggers this stutter). Please let me know if I can help with anything else.
Bug 1608485 Comment 23 Edit History
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Wasn't able to reproduce the issue on 2 other different systems. One is a Dell laptop with Intel HD 4400 (20.19.15.4531 driver version), and the second is a desktop PC with integrated ATI Radeon HD 3000 graphics (8.970.100.9011 driver version). Both performed as expected either on 1080p60 or 1440p60, 4k60 was not testable due to hardware limits. The only system on which I reproduced it had Intel HD 630 with latest driver installed and only on 4k60 (maybe there was a recent update for these gpu's which added an incompatibility and triggers this stutter). Please let me know if I can help with anything else.