I also thought this was a bug before I realized you can cancel tag-along during the attach by pressing 2 again, so if you're mashing 2 trying to find a tag-along target you'll cancel it if you're not careful, which I'd be willing to bet happened here.
I'm not 100% sure but I think that this happens when the build-maker has a different resolution than you, so it looks fine on their screen when they publish it but it can look like this on other resolutions. Best option is to deal with it or hit copy + edit and resize the boxes, though you'll...
Ever since the initial old gods new blood update, I get bad stutters in actual games when opening either the shop, or the tab HUD. Doesn't seem to happen in hero testing/the hideout, but is quite bad in-game. I almost exclusively queue in parties if that's relevant. Here are my video settings...