Hello! I am also seeing this problem. The Gallery is showing in one single column with multiple rows instead of one row and multiple columns. I’ve cleared the cache and tried to solve it in troubleshooting mode. The gallery functions properly when in troubleshooting mode using Twenty Nineteen Theme. I’m using the latest GeneratePress Theme and Premium plug-in. Please help! Thanks.
I actually figured out a fix by simply installing the Gutenberg plug-in (https://wordpress.org/plugins/gutenberg/). Not ideal to have another plug-in running, but it solved the problem. If there’s another way to fix it, I’d love to know!