Playing a sequence using a lot of instruments presents a different challenge than sustaining a long note. Obviously your system has the bandwidth to feed the multiple simultaneous short duration data bursts that are required by your sequences. However, sustaining a long note, even a single one, is another kind of challenge. Many things are capable of interrupting the data stream momentarily. I\'d look for unneeded software running in the background, interrupt conflicts, modem or network issues, even video acceleration etc. as possible causes.