Thumbnails don't appear in flash website on Safari

Project thumbnails don't appear on my website homepage, except for the first one, when using Safari. If I hover over where the thumbnails should be the project titles appear but the thumbnails don't. If I click a blank thumbnail the portfolio images appear and I can scroll through these normally. The problem is only on the homepage. Any ideas?

OS: 10.12.6

Safari: 11.0.1

Flash: 27.0.0.183