I have a question about Blackburst sync signal , When I use the engine output, sometimes the output picture jitter will appear, and later I found that it is caused by the synchronization problem

. However, I don't know why, as long as I use these two video cards, this problem will occur, but the frequency is not very high.,So ,what's the situation? How to avoid it?

Engine working environment :

OS : WIN 7 PRO 64 bit
Engine : Engine 64bit
Video board :Matrox X.mio3 OR Matrox DSX LE4 Driver :