Hello Gary,
Thanks for writing in!
If you update your WordPress core, then you will have to update the theme and all the plugins to avoid any issues because in each of the major updates of the WordPress core, it introduces, new features, bug fixes, security and a lot more. And this is the reason why theme and plugin developers update their products too. Developers needs to stay on top of the latest WordPress standards.
By the way, I have checked your sites associated with your licenses and I noticed that two of your site is throwing a JS error. This could affect your site and the experience in using X theme or Pro theme. The error might prevent you from previewing your site in the editor. I have figured out the source of the JS error and it is caused by your custom JS. I would suggest that you remove this JS code first:
<script type="text/javascript">
document.write(new Date().getFullYear());
</script>
And replace it with only this:
document.write(new Date().getFullYear());
You do not need to insert the <script> tag because when outputted in the front end, it will be wrap with the tag automatically.
Hope this helps.