I have solved the issue, it was my litespeed cache plugin. After disabling the plugin, the sidebar started populating correctly. Very weird.
Well, I’ve noticed that my sidebar is blank again… and I no longer have the litespeed cache plugin… so no idea why.
Ok, disregard… I found the problem. I had customized the template menu-sidebar-section.php.
I had:
<?php echo $this->current_section->name; ?></div>
where the original file from the latest version of the plugin is using:
<?php echo $this->current_section->title; ?></div>
Updated my template, all is good.