There's seemingly no way to message eBay directly to give them a bug report, so I'll report it on here.
When sorting by Cheapest on my Android mobile app, it doesn't fully sort by cheapest, it'll throw in a few more expensive ones for some reason. Sometimes the cheapest option isn't even shown first. I've attached a screenshot of a recent search.
It makes it hard to trust eBay, I feel like I need to check all the options now to find the cheapest... Which is probably the idea.