eBay delivers the live price to 3Dsellers for each item. Their system does not account for or specify the Sale Event + markdown promotion percent.
We will implement new features to manage Markdown and other promotions as soon as possible.
For now, it is best to pause campaigns before making price adjustment. Else, your actual prices could be decreased significantly.
Vote for this feature to stay updated about Sale Event +markdown features on 3Dsellers: https://feedback.3dsellers.com/new-tool-ideas/p/markdown-and-discount-manager-and-feature