Well, since there appears to be little interest in this problem, I will record what I'm doing on my own in hopes that someone else w/the same problem sees this. The reason I know that it's weblink.api that's causing the problem is because when I remove it from the plug ins folder and place it in an Optional folder that I created, performance returns to normal. This is fine, but without weblink.api the commenting feature is all but useless and I rely on it heavily to enter edits into the source document.
I used the Shared Review feature in another project, and still had documents live. I thought that the application might still be reaching out to those old review copies. So I ended all reviews and removed the documents from my review list (that feature is very slow, too, btw.)
That didn't help.
I have a workaround where I open the plug_ins folder and click and drag weblink.api to my Optional folder so that the document opens properly. Then I copy the PDF to another computer and so I can view the comments properly and make my changes. It's tedious, time-consuming, and somewhat error-prone, but it's better than what I've been doing.
I also print out comments only to PDF, close Acrobat Pro, remove weblink.api, and then open the comments up. Then I can copy and paste the edits. Also tedious, but better than trying to work with the sluggish performance.
I'll keep this thread open for another week or so.