1/2 to 1 second delay between mouse command and actual execution of command.

Hi,
I now have a 1/2 to 3 seconds delay between mouse command and actual execution of the command on the screen.
This delay makes it very difficult to place notes on staff in correct position, resulting in frustration and confusion.
I have the problem only in one score, the others are OK. I have spend about 25 hrs on this score which is also my own composition, thus subject to copyright. Is there any way I can correct it without having to print it and re-program it into an new score?
I have tried to copy the score into a fresh score but it also copies and pastes the problem into the new file.

I also have problems to stabilise the program as when I first start the program up. The whole program disappears so I have to reload it, sometimes up to 6 times before it becomes stable.
My operating system is Linux Ubuntu. believe that I have one of the latest musescore releases which I updated about 6 month ago.
please can you help me, as I am not very computer savy.
with kind regards, Victor.
victorgrotaers@bigpond.com