When I upgraded to GeneratePress 2.3, the mobile menu disappeared (I’m not using the Off Canvas Menu). I have 2.3 installed on the staging site (starts with “https://staging2.”) but the live site (without “staging2.” is running 2.2.2 and it works fine). I’m not using the SVG icons. I’m using GP Premium 1.8.3.
Disabling the SG Optimizer caching plugin resolved the problem. I did some debugging and found that enabling the plugin but turning off the optional feature to combine CSS files resolved the problem.