Long time ... Just subscribed again.
I have a problem after updating Jooma and Gantry to 3.10.3 and 5.5.3 respectively.
The submenus I use just disappeared. I use Menu modules that show only the menu levels Level 2 under a Menu which uses only Level 1 menu items.
After I noticed the problem I updated the Milano Template to your current version 1.12.0. The problem remained. I recompiled CSS in the Base template, no errors but problem remained. I cleared all Server, Gantry, Browser ... caches after the installation. Problem remained. I tried it on Firefox, Chrome, Opera and Safari. It's a server problem. I also noticed an error in the web-console:
Source map error: Error: request failed with status 500
Resource URL: https://hai.swiss/media/gantry5/assets/js/main.js?617d3a4c
Source Map URL: main.js.map
All the rest of my site is (or seems to be) working as before. Some gutters grew significantly but I think I can fix that myself.