MTLBlitLoops.java

static void IsoBlit(SurfaceData srcData, SurfaceData dstData,
                        BufferedImage srcImg, BufferedImageOp biop,
                        Composite comp, Region clip,
                        AffineTransform xform, int hint,
                        int sx1, int sy1,
                        int sx2, int sy2,
                        double dx1, double dy1,
                        double dx2, double dy2,
                        boolean texture)

method has a check

if (rtt && oglDst.isOnScreen()) {

and there is a RQ.FlushNow() call if the check passes.

This conditions currently is being evaluated to true always. This could be attributed to unimplemented stuff or work in progress.

This hogs AWT-EventQueue thread to the extent the applications becomes slow responsive.
My suggestion is to comment out this code till the time we actually need it to implement the specific case that the the current if condition handles.