I have a feeling this is already reported somewhere due to how common it is, so I searched many times but still found nothing. Provided as much information as I could, in case it was and one was missing it.
That could be true, I have picked up the new commands only recently (used the old format for years however) and I have not thought of everything, such as that. Will have to try it out and see how it goes. Thank you however! Even if not a bug I still needed a fix for this. EDIT: Can confirm that in fact did make it work properly. I tried everything but using both as and at, guess I overlooked that. Still open for debate if this is a bug or not, but at the very least there is a way around it if there is. Many thanks!
This seems like an issue that should be very common, and reported already, but I have searched many times and found nothing.
The dust and smoke particles has also become significantly more laggier than when it was in 1.12, in 1.12 you could have 1000+ on a repeating command block and only have minor issues, in 1.13 with that many particles fps drops to 1. Extreme case, but only mentioning it because that is what my testing did
In my testing it also appeared that in 1.12 when a large amount of particles were displayed, their lifetime appeared to be shortened. Not sure if this is from lag or if it was intended, but I could not see this happening in 1.13. This may be contributing to the issue, but the main reason has been found above.