Steps to reproduce:
Install Dark Reader, click extension icon & enable Dynamic mode under the "More" pane (enabled by default).
Multiple websites (e.g., heb.com, wsj.com, economist.com) will briefly render before turning blank & laggy. The extension icon also turns inoperable on the same tabs.
Switching to different filter modes for Dark Reader resolves the bug.
Safari smoothly renders the same websites with Dark Reader for Safari enabled in Dynamic mode.