I have been ripping my hair out trying to figure this out. So far I have spent about 6 hours Googling and trying different options with no results. Here is the link to the site: http://www.postbeam.com.au I inherited this site so I don't know exactly how it was built. I have updated to Joomla 3.8.8 from 3.7 and updated the JT3 framework plugin. Since then the sub-menu items will not display only on the homepage. The menu works perfectly on every other page.
If you look on the homepage the menu that contains "Building Materials","Energy Efficiency" etc, these all contain sub menu items but the do not display on hover. If you go to the about page here: http://www.postbeam.com.au/about-us/about-post-beam You will see how the menu should function.
I have tried the "rebuild" option in the menu admin panel. I have done the extension > database fix as well. There is no javascript error in the console that I can see. I have Googled the hell out of this to try and find a solution with no luck.
Thanks in advance for any advice you can give.
It could be a problem with your custom template but first I'd suspect a module or plugin that is interfering with the menu, but isn't published or active on the about us page. Unpublish them and republish them one by one to find the source. Create a backup before you do anything, use Akeeba backup.
Note that your home page took >46 seconds to load for me. That me be a symptom or an entirely different problem to solve.