Preview 'Smart Lasso' wonky

I can't get Preview's Smart Lasso tool to work as it used to. The only way I can think of to get that thick border around my chosen outline is to hold the mouse key down with Sellotape or something. Even then I don't know if it will work properly. I can't keep the mouse button down long enough to complete an outline. I need to break every so often.

I find that the slightest bump and the mouse button releases so one loses one's place forcing one to start over again. I can start drawing the "thick red border' but if the slightest drop in pressure of my finger on the mouse button happens, then either entire screen gets selected, or it draws a straight line back to the origin. I used to able to trace whatever outline I needed and it would leave a line with drag points at various intervals.

No more it seems. It's now easier to scan, print and cut out the image with scissors then rescan. I'm sure you will know what I mean.

As for the comments about Beta Testing. I can find no evidence of this whatsoever. I suspect that SL has been brought out before it was ready.