Insta360 One R 1-Inch: Recording in h.264

When I record with h.264 enabled, the resulting video has a weird 'pulsation' effect that occurs every 1 second throughout the video. It almost appears as if the noise or grain pattern is shifting during these recordings. However, if I record in h.265, that effect is not apparent (although the video still seems excessively noisy to me, even with grain reduction turned on during export).

To note, I've been recording in 5.3k and exporting using the desktop app. I've tried full manual and auto settings, exporting to h.264, h.265, ProRes, turned on/off ColorPlus and Grain Reduction in various ways, enabled and disabled log recording, and its only apparent when recording in-camera using h.264.

Also, the micro SD card I'm using writes at a sustained 86MB/s.

I haven't seen similar examples of this online or in any discussions, so I'm wondering, is this is unusual behavior in my particular device?