Hello
I have experience with wordpress/wordpress troubleshooting. I could investigate your site, but implementing a fix could be more than the budget for this project. The simple solutions are to find the plugin that causes the many issues and remove it, but that might loose functionality of the site. What I can do is to take a look and remove all the unnecessary plugins, check the database size, and come up with a plan on how to fix it if it is not straight forward.
I would need to see the site/ have access to admin area to be able to check it.
Regards
Eva