Quick temporary fix for this for others.
This file appears to be the reason for the problem
/plugins/eventprime-event-calendar-management/includes/events/views/single-event/description.php includes/events/views/single-event/description.php
Make a folder in your theme folder:
/themes/your_theme/eventprime/events/single-event
Add a file named description.php with this content:
<div class="ep-box-row ep-my-2">
<div class="ep-box-col-12 ep-text-secondary" id="ep_single_event_description">
<?php $content = apply_filters( 'ep_event_description', $args->post->post_content );
$content = wpautop( wp_kses_post ( $content ) );
echo $content;?>
</div>
</div>
The additional line
$content = wpautop( wp_kses_post ( $content ) );
tells wordpress to render line breaks and paragraphs from your description in html code. Ref: wpautop wp_kses_post
This ‘fix’ will survive a new release by EventPrime, so when they do release an update that corrects this major issue, please remove this from your theme folder.