You are operating under a misconception, that the icon exists as a "interrupt me" notification. That's not what it is. It is an icon for QUEUED mystery.

And by queued I mean something that will not be resolved immediately.

Fact of the matter is, the server does NOT wait for you to act against any queued action. queues are resolved ASAP.

Now, when the queue is made during another action (especially during a long animation like during a chase chain) or it's not the correct "turn" for it to resolve, it cannot resolve immediately, so the icon stays around and give you time to interrupt.

But if the queue is made right before the action can be made, it is resolved immediately and you won't have a chance to interrupt.

The only difference between prompt and non-prompt for this is that prompt may be resolved between any action whereas non-prompt can only resolve at a specific moment in time. Therefore, it might not get to resolve until other actions have taken place.

This fact in and of itself is not related to lag.

It's also not a bug, thou potentially a design flaw as interrupt/CC are meh as a result. There are ways to improve the design but that requires serious change to battle mechanic.

The problem of lag is a different issue altogether, That's a matter of server state, specifically when you are behind the server so whatever you see at the time have already happened and whatever you order will only happen sometime later. I don't think that's your point of complaint here.