Please check that, on the 23rd of May, you should have received an eBay message with the subject "We're updating our Promoted Listings program", which says:

Starting from 24 June, items listed on ebay.com.au, ebay.co.uk, ebay.fr, ebay.it, and ebay.es and promoted with a general strategy will use the following attribution definition when reporting sales and charging ad fees:

An attributed sale will be when any buyer purchases the promoted item within 30 days of any click on the ad, regardless of whether the buyer themselves clicked on the ad. The item must be promoted at the time of click and the time of sale. The seller will be charged the ad rate at the time of sale.

That's because of the new pricing structure which came into effect on 24th.

Your percentage of promoted listing sales have probably not increased at all, but you are now being charged the promotional fee even if someone other than your buyer has clicked on the promoted listing. This didn't happen prior to 24th June.