It was though to find code that actually replicates this issue, because at first it seemed to happen quite randomly. There might be more cases then this one.

It seems to happen when passing/storing playerinfo objects to multiple functions; I'm guessing they go out of scope when the first function finishes execution:

import command_c

def h(playerinfo, command):
    test(playerinfo)
    test(playerinfo)

def test(playerinfo):
    e = playerinfo.get_edict()
    e.get_index()
    print(e)

def load():
    command_c.register_client_command_filter(h)

def unload():
    command_c.unregister_client_command_filter(h)

Running this code will result in:

<entity_c.CEdict object at 0x12345678>
(Traceback here)
RuntimeError: access violation - no RTTI data