I'm using 5.6.5 and the [event_form] shortcode, and it just seems ... broken.
For starters, the page I drop it onto does this:
http://www.nhmgscitadel.catchthispilum.com/NHMGS/submit-an-event/
(notice the broken style tag at the top ... that's not me; this is just the default form shortcode and it breaks.)
Code-wise (view source) this is what it's doing:
<div class="et_pb_text et_pb_module et_pb_bg_layout_light et_pb_text_align_left et_pb_text_1"> ” background_layout=”light” text_orientation=”left” use_border_color=”off” border_color=”#ffffff” border_style=”solid”]<div class="css-event-form">
<form enctype='multipart/form-data' id="event-form" method="post" action="/NHMGS/submit-an-event/">