I have a pretty complex system of grouped metaboxes. They show/hide based on a template dropdown and generally, it all works really well. Over time, though, the admin has slowed to a crawl. I've been taking other mitigation steps (increating memory limits and max_execution_time, limiting the WP heartbeat, etc).
However, I believe that it's the metaboxes that are taking extremely long to load. And in the console, I can see tons of messages relating to things like "Found 2 elements with non-unique id". I'm wondering if anything can be done to help with this. My content editors are at their wit's end with the slowness and I'm out of ideas for what to do to help them.
Please share the code that created the group, some screenshots of the console tab, and the list of plugins active (in Tools > Site Health > Info > Active Plugins). You can also deactivate all plugins except Meta Box, MB extensions and recheck the issue.