Skullcandy is... generally not the way to go for bluetooth audio. Especially if they're an older pair.

You likely have a fair amount of latency. Try a game you know well and A/B it with and without and you'll likely notice it.

When watching on stuff like YouTube or Netflix, the app will automatically compensate playback so you won't really notice the delay.

To cut latency down, you'll want an earphone with a low latency or gaming mode you can toggle. It doesn't look like the transmitter you bought lists supported codecs, so it's probably just SBC and AAC (maybe). Not Apt-X Adaptive or anything. Something like this is decent for that (for budget pairs).

Also, maybe if you added some type of material on top of the transmitter it'll grip the bottom of the MM+ a bit so it doesn't swing around.