500 error on just about every site

hello guys,

OK - sad question.

my server went from self-managed to managed.
when it did, they tweaked some stuff to standardize my pimped out server for ease of maintenance.

what happens now is that when i go to almost any of my sites, i get a 500 error, the server can't handle the request.

when escalating this to the hosting kids, they disable some plugins, and do a random reload test, and then say that they fixed it.

but - 1 - i can't just live without functionality. i mean, really?
and 2 - the problem only happens on wordpress.
it's especially messy when trying to go to /wp-admin, as opposed to the home page.

can you please have a lookie see? i'm making extra notes of other sites influenced in the support access space on the site itself.