I managed to fix this temporarily by amending class-template.php inside wp-content\plugins\wpforo\wpf-includes.  I also kept the 'Home' icon for consistency, rather than it changing to the forum name when it gets to the forum home page.  (Note that my site is in development so this will probably need more extensive testing) I replaced lines 1048 to 1051 (inclusive) with:

<?php break; 
    default: 
	$count = 0; 
	if(isset($forumid)) : ?>
        <?php $relative_ids = array();
        WPF()->forum->get_all_relative_ids($forumid, $relative_ids);
        foreach( $relative_ids as $key => $rel_forumid ) : ?>
            <?php $forum = wpforo_forum($rel_forumid) ?>
            <?php if(!empty($forum)): ?>							
		<?php if($count == 0) ?>
		    <div itemprop="itemListElement" itemscope="" itemtype="https://schema.org/ListItem" class="wpf-item-element wpf-root<?php echo ( !isset($forumid) ? ' active' : '' ) ?>"><a itemprop="item" href="<?php echo ( !isset($forumid) ? '#' : wpforo_home_url() ) ?>" title="<?php esc_attr( wpforo_phrase('Forums') ) ?>"><i class="fas fa-home"></i><span itemprop="name" style="display:none;"><?php wpforo_phrase('Forums') ?></span></a><meta itemprop="position" content="1"></div>
		<?php $count ++; ?>								
                    <?php if( $key != ( count($relative_ids) - 1 ) ) : ?>
                        <div itemprop="itemListElement" itemscope="" itemtype="https://schema.org/ListItem" class="wpf-item-element"><a itemprop="item" href="<?php echo esc_url( $forum['url'] ) ?>" title="<?php echo esc_attr($forum['title']) ?>"><span itemprop="name"><?php wpforo_text($forum['title'], $lenght) ?></span></a><meta itemprop="position" content="<?php echo $key+2; ?>"></div>
                    <?php else : ?>
                        <div itemprop="itemListElement" itemscope="" itemtype="https://schema.org/ListItem" class="wpf-item-element active"><span itemprop="name"><?php wpforo_text($forum['title'], $lenght) ?></span><meta itemprop="position" content="<?php echo count($relative_ids) + 1; ?>"></div>
                    <?php endif ?>
                <?php else : ?>
                    <div itemprop="itemListElement" itemscope="" itemtype="https://schema.org/ListItem" class="wpf-item-element active wpf-root<?php echo ( !isset($forumid) ? ' active' : '' ) ?>"><a itemprop="item" href="<?php echo ( !isset($forumid) ? '#' : wpforo_home_url() ) ?>" title="<?php esc_attr( wpforo_phrase('Forums') ) ?>"><i class="fas fa-home"></i><span itemprop="name" style="display:none;"><?php wpforo_phrase('Forums') ?></span></a><meta itemprop="position" content="1"></div>
                <?php endif ?>
            <?php endforeach ?>
        <?php endif ?>
    <a href="#" class="wpf-end">&nbsp;</a>
<?php endswitch; ?>