Please correct me if I'm posting in the wrong spot: I had slow 2D rendering on a Lenovo P15 Gen 1 on several versions up to 21.6, then 21.6.1 seemed to fix the issue. With 21.8, the issue has returned. The usual 2D render settings have no effect on the behavior (it's as if it's stuck on iterative draw). Paging through PDFs big and small becomes a total chore as the page up/down keystrokes easily get ahead of the page rendering, and since the keystrokes are stored, the pages will continue incrementing well after you stop keying. Is this a known issue?
