2) Check load time and number of queries in the top bar. Load time has "s" and queries "Q"
3) Disable all WPML plugins and check load time and the number of queries now
4) Disable all other plugins and leave active only WPML plugins, switch to WP default theme. Check again. If it works fine here, enable back 1 plugin by 1 and at the end your theme, to see what causes issue.
Please let me know how it goes and shares each result with me.
Since you are also using a custom theme and other plugins, please check and next and let me know the results:
Disable all other plugins and leave active only WPML plugins, switch to WP default theme. Check again the load time. If it works fine here, enable back 1 plugin by 1 and at the end your theme, to see what causes issue.