The trigger is document.visibilityState, not headlessness. Sites hydrate feeds only while the document is visible, and a headless browser is always hidden — but so is a real window whose tab isn't the one in front.
Measured on one profile within the same minute: hidden, the feed stayed at 2,794px and 3 posts however far it scrolled; brought to the front, 20,611px and 28 posts as soon as it moved.
Two things fix it: tick Run visibly on the schedule, and make the process bring its tab to the front as its first step (switchTab). The shipped Reddit warmup does both — under the scheduler it reads 20 to 24 posts a page where it used to see 3.
More detail: https://parallel-browser.com/learn/headless-browser-detection
Measured on one profile within the same minute: hidden, the feed stayed at 2,794px and 3 posts however far it scrolled; brought to the front, 20,611px and 28 posts as soon as it moved.
Two things fix it: tick Run visibly on the schedule, and make the process bring its tab to the front as its first step (switchTab). The shipped Reddit warmup does both — under the scheduler it reads 20 to 24 posts a page where it used to see 3.
More detail: https://parallel-browser.com/learn/headless-browser-detection