Looks like some anti-scraping on day 1, and really twisting the knife for Twitter:
https://www.threads.net/t/CuVZfoihkcF
Text follows for those without the app, RT from Adam Mosseri, head of Instagram (original tweet from Jesse Chen):
FYI for everyone, we’ve set our rate limits to “generous” bc we believe you have the right to see more than 600 posts in a day here.
if you encounter a rate limit block and you’re not a scraper, please let us know. thanks!