This appears to be a problem in both the web version as well as the desktop app. Whenever you scroll back into the messaging history (doesn't matter if its recent or not), it takes an incredibly painful amount of time for the messages to load. I went to a training session recently where Teams was being touted as this end-all-be-all that was better than Slack but this one simple thing can't even be sorted out. There's a UserVoice post about this with 230 votes but like with any UV forum/discussion topic, you need somewhere in the neighborhood of 9999 votes on your topic for it to get any kind of traction from the development team to even read or recognize that issue as a problem.
Seriously, Microsoft. You guys want to tout this as a tool to use for collaboration and you have technology events singing its praises but I can't be sure how you use it internally if this kind of glaring problem is just outright ignored both on the web and desktop versions. Its a dealbreaker for me. I can't imagine rolling this out to 300 users when only 3 of us in IT are having this problem.
Yup, it's painful experience, it loads the messages from the azure chat service and this process can definitely use some improvements. Lately, it's failing to even display the "placeholders" for the messages, so I can keep scrolling up in a completely blank screen, without even an indication that there are older messages. And 30 seconds later they start popping up...
@sbellad unfortunately the problem with the uservoice feedback forum is that this very problem has been in existence over there for at LEAST two years with zero response from the team responsible for this product. Its tough to tell when it will ever get on their radar.