Check if SDDC Manager is connected to the Internet.
If this is an offline environment, please follow "Offline bundle download fails to update LCM 2.0 manifest" here:
After re-reading you message, I think this can also be a browser cache issue. Try deleting your cache, log out/back in to SDDC Manager, and try again. Or try another browser.
SDDC manager is connected to the internet. I can see the new bundles available for download. They appeared yesterday. Also, I hoped briefly that it was a browser cache issue. But after deleting the cache and relaunching the browser there was no change. Unfortunately, in the environment, which is accessed currently through a jump host I don't have another browser that I can try. However, my instinct tells me this is not a web browser issue.
It turned out that there is a bug in vcf 4.2 that was causing logs not to rotate. I had a huge log file that filled up SDDC manager root. Once GSS figured this out and got rid of it everything went back to normal.