wp_remote_get doesn't work on plugins_loaded hook

I’m trying to use wp_remote_get as early as possible, and it doesn’t seem to work on the plugins_loadedhook - I get this error:
AccessDeniedAccess Denied964CDD2DEBC15BD3UXzVx0pX3wyBKb+DczsqA/EqHjwkyMoA6F+v17lsII+0JVVxAdq924WGa2zLpp1I

When I use it on the init hook it works just fine. Any ideas?

Bonus questoni: if I’m executing code directly in my plugin file (not in any hook/filter), is there a corresponding hook/timing on which it is executed? For example, if I just have a plugin file with echo 'hi';, when in the grand scheme of action hooks is that going to echo? Thanks!