Child Theme Widgets Now Below all Content

You are not using a child theme. You appear to be using a standalone custom theme.

nothing to do with the upgrade.

caused by an unclosed div in your latest post ‘Learn “Beautiful Things” by Gungor’:

edit that post, using the html setting of the post editor;
find:

Learn Guitar Songs!<br>
Artist: Gungor<br>
Album: <em>Beautiful Things</em><br>
Song: “Beautiful Things”</p>
<div style="clear: both;">
<h3>Important Notes</h3>

remove this line:

<div style="clear: both;">

also, the h1 tag of the site title is not closed properly on your front page;
edit header.php;
compare your code with this section from the unedited Twenty Ten:

<<?php echo $heading_tag; ?> id="site-title">
					<span>
						<a href="<?php echo home_url( '/' ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a>
					</span>
				</<?php echo $heading_tag; ?>>

and fix it.

Thanks for the help on the unclosed div alchymyth! That actually isn’t the first time I’ve done that…hopefully I’ll remember this time

I’m not sure I follow on the suggestion to edit my header.php…I checked the original twenty ten and my child theme and it looked the same. I’m still learning php though so…can you clarify?

the validation report reports a missing </h1> tag:

Line 64, Column 28: Unclosed element h1.

https://validator.w3.org/check?uri=http%3A%2F%2Fblog.igniteguitar.com%2F&charset=%28detect+automatically%29&doctype=Inline&group=0

which is often caused by wrong edits to that particular section in header.php;

if you would like me to check the code, you can paste the full code of header.php into a pastebin.com and post the link to it here – HOWTO

It would be appreciated. Thanks. Here’s the header code —
https://pastebin.com/ZZRgKWDM

this is missing between line 90 and line 91:

</<?php echo $heading_tag; ?>>

this section should look like so:

</span>
</<?php echo $heading_tag; ?>>
<!--                            <div id="site-description"><?php bloginfo( 'description' ); ?></div> -->

Been busy…but was just able to make those edits. Thanks for your help!