Hello I am facing a problem with taxonomy_advanced where it does not bring the taxonomy terms, however if I set it to 'ajax' => false, the field will start to work.
My environment is
Wordpress 5.4
Metabox 5.2.10
Php server 7.4.1
Could you please deactivate all plugins except Meta Box then check the problem again?
I've tested again on my local site and the field taxonomy_advanced works as well as ajax enable. You can also open the Inspect Element tool of the browser and check the tab Console to get some information.
.
