No updates from Roku support yet, but they said they're continuing to investigate. Also, @DaddyS I've already taken a photo of the issue and sent it over to Roku support, attached here, so no worries on getting the shot. Thanks for the update. Picture of the bar while watching Netflix. The bar is stuck on the Netflix logo opening shot for this episode of Tiger King, hence the bright neon colors.
In the meantime, the issue has occurred again after about 4/5 days of using the TV nightly, this time on the Web Video Caster app. Once again, the bar stays stuck on the first few frames of the video, and only disappears when I exit the video, but not the app itself.. I've sent an update. I hope Roku addresses this soon. I doubt this is a hardware issue at this point, which is a relief as I likely don't have to return or exchange this TV.