Sprint as a function was changed a long time ago, and while it was never explicitly mentioned in any patch note or change log, it feels like it activates as a macro does now.
Before it was very snappy and worked like any other ability. Then the change happened (I think it was when TP was removed since Sprint used TP as a resource) and the action feels delayed like a macro would as it won't always go off when the GCD is rolling or you're otherwise in an animation lock.

So while maybe support can offer you more help, I just wanted to throw this out there and set your expectations a little low, sadly.