Many thanks for the reply. I did lots of tests on several domains and finally the following was resolved:
I dont know how and where from, I installed GTP version 2.0 on this specific network website (http://sunilverma.org). It was creating all problems. I went back to wordpress.org/GTM site and found that the latest verrsion released there is 1.9.5. How come I had version 2.0, I have no idea. I then completely un-installed GTM V2.0, deleted it and re-installed again from dashboard. This time it was V 1.9.5. It is working great everywhere, on main domain, network domain, mu domain. Great!
You can check that it is no more distorting homepage and also the activity plus plugin is working fine.
Many many thanks again.
Dr S K Verma