Thank you for contacting WPML support, I'd be happy to help you with this issue.
It could be an issue with slowness caused by one of the plugins not being compatible with WPML or some theme code. Can you please follow the next steps and let me know how it goes:
Please make a backup before proceeding.
1) Install the Query Monitor plugin (https://wordpress.org/plugins/query-monitor/).
2) Check the load time and the 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.
4) Disable all other plugins and leave active only WPML plugins, switch to a WordPress default theme. Check again.
Please let me know how it goes and shares each result with me and read more on the documentation https://wpml.org/tutorials/2019/10/analyze-performance-issues-with-query-monitor/