I can't say that I've been having trouble leaving feedback, but if the problem still hasn't gone away by the time you read this reply try logging out of eBay UK and log onto https://www.ebay.com, which is the American version of the site. See if you can leave feedback from there - if the problem is down to a glitch which is specifically affecting the UK site then by logging on to one of eBay's other websites you may be able to get around the problem, in which case you ought to be able to leave feedback for the people you are trying to leave it for.
