With synths... it can have a pretty big effect on the playback. People using the factory realtecs tend to have problems playing some synths. I've seen some folks having all sorts of issues due to the factory cards not handling the synth load in real time. Your card is a good card though so it is not likely to be the problem.
with all the recent changes to X1 and the 4 or 5 upgrade/fixes.... the issue might be a bug. I've seen a number of actual bugs reported here. I don't have that synth so I can not load it to check.
Start with a fresh re-boot of the computer and the sound card.... then try it again. Could be a glitch. When in doubt, reboot first. That's my standby when I have weird things happen.
If that doesn't solve it.. then more detective work is in order.