Thanks, and sorry about that — this was a regression in a recent version. I've fixed this in the latest Zotero beta, and the fix will be included in 5.0.85. (If you want, you can install the beta, import the OPML, and switch back to the release version.)
@philobib: Same as above. Can you either post a link to a sample OPML file that doesn't work or email it to support@zotero.org with a link to this thread?
I'm using 5.096 and having the same problem. No error message but the feeds are not imported.
It was exported from feedly.