I first noticed the issue on my forum where I’d used CSS to make the Desktop View fit on mobile screens to get the embedded posts for quotes. It worked fine for months and I only just noticed I no longer had a topic progress bar on small screens. Here’s how it acts on my site (this is in Desktop View):
Yeah I’m seeing the same thing… seems like performance took a hit somewhere? (also noticed the avatar/topic layout wraps at a specific width, investigating that)