The comment feature in the righthand panel of the design spec links is not appearing, and when I try to view previously posted comments I get an error "We're having trouble loading the comments for this asset. Please try refreshing the page."
Sorry to hear about the trouble. Could you please try unchecking the "Allow Comments" checkbox, clicking "Update", then checking "Allow Comments" and updating again (basically turning it off and on again from the panel on the right.
In case if this doesn't help, please share a few more details like:
The version of XD & OS.
Is this happening on a specific file or multiple files?