Mouse Delay and Hover Intent not working for user 1

I have a strange issue on one site. It is a multi-site site and the parent site works fine for this aspect.
I have 3 tiers under one item of the menu. If I am logged out, or using any other account, including another account I created to test also with admin permissions then mouse delay and hover intent work fine. If I am using the primary admin account - i.e. user 1 - then these functions appear to be disabled and the third tier disappears before I can get my mouse over it. The third tier also is narrower under this account with entries appearing on two lines for most of them, whereas in any other account they appear as one line (see screenshots attached).
Please can anyone advise what is causing this and how to fix it?
Thanks
Martin