Hi Aaron.
I have the same problem, I have WordPress 5.5.1 and Avada Theme. I inspect the problem with the console in inspector browser.
The problem show:
XHR POST https://mysite.com/wp-admin/admin-ajax.php
State: 400 Bad Request
I tried the solution installing https://www.ads-software.com/plugins/enable-jquery-migrate-helper/ and still show the last message about admin-ajax.php and next this message:
JQMIGRATE: jQuery.fn.attr(‘checked’) might use property instead of attribute jquery-migrate-1.4.1-wp.js:56:12
console.trace() jquery-migrate-1.4.1-wp.js:58:13
jQuery 4
migrateWarn
attr
X
attr
<anonymous> https://mysite.com/new/wp-content/plugins/toast-stick-anything//backend/script.js:8
jQuery 9
dispatch
handle
(Asíncrono: EventListener.handleEvent)
add
add
ra
each
each
ra
on
<anonymous> https://mysite.com/new/wp-content/plugins/toast-stick-anything//backend/script.js:4
jQuery 8
i
fireWith
ready
J
(Asíncrono: EventListener.handleEvent)
promise
<anonymous>
<anonymous>
<anonymous>
I run the plugin Health Checker and everything is fine in my site.
I hope this help to solve the problem.
Thanks