Rate of Voice Over is Everchanging

Hi All,

I recently updated to MacOS 10.14.6.
I notice that the RATE of voice over is changing a lot while I use or switch windows or Apps.

If I change the rate to 70percent or higher, the actual voice over rate is not as expected.

Also, some items can not be read at once, I have to go back and forth to that particular item for it to be read by voice over.

Has anyone experience the same?