Gameplay effect isn't always firing from client side

I’ve been working to learn the GAS system and for the most part it seems fine, but when I simulated network lag (average), client abilities seem to not always hit. The lag should not be such that they’re outright getting lost, and there’s also a noticeable… well, lag, on the abilities being triggered. About half a second from input to the ability being activated.

Here’s a video example:

The ability itself:

Code itself is a mix of c++ and bp. I’m pretty familiar/comfortable with c++ and do most of my stuff in it, but I’m totally new to GAS so I’m trying to start with the basics and then eventually move most things (if not all of this) into c++ once I’ve gotten a good understanding.