Swapping templates hangs site

[mattpettefer]

After selecting a different template, the entire site hangs for over a minute with disabled update button before "Updating..." begins.

There are no errors other than some assets being served over http rather than https from plugins. On the occasion that a template had a block error, the behavior was exactly the same as when there are no errors in the template. Same whether there is a template part in the template or not.

Template example:

<!-- wp:template-part {"slug":"header","tagName":"header", "className": "site-header2020"} /-->
<!-- wp:group {"tagName":"main","layout":{"type":"constrained"}} --><main class="wp-block-group">

    <!-- wp:post-content {"className":"legacy-post-padding"} /-->

</main><!-- /wp:group -->

Theme.json snippet:

"customTemplates": [
		{
			"name": "page-no-title",
			"postTypes": ["page"],
			"title": "Page No Title"
		},
		{
			"name": "page-with-sidebar",
			"postTypes": ["page"],
			"title": "Page with Sidebar"
		},
		{
			"name": "page-wide",
			"postTypes": ["page"],
			"title": "Page with Wide Image"
		},
		{
			"name": "single-with-sidebar",
			"postTypes": ["post"],
			"title": "Single with Sidebar"
		},
		{
			"name": "single-academic-pages-legacy",
			"postTypes": ["academic-pages"],
			"title": "Academics Pages Legacy Padding"
		},
		{
			"name": "single-academic-pages-legacy-header",
			"postTypes": ["academic-pages"],
			"title": "Academics Pages Legacy Header"
		},
		{
			"name": "single-academic-pages-w-title",
			"postTypes": ["academic-pages"],
			"title": "Academics Pages with Title - M.S."
		}

	]

[mattpettefer]

To clarify, the button doesn't break the first time templates are switched - update needs to be clicked but it still hangs for 30 - 60 secs and then taked 1+ minute to update.

This is not the case if I leave the page on the default template.

[poena]

Hi @mattpettefer

Does this happen on all post types or only the custom post types?
Does it happen without custom plugins and with a default theme active?

Can you share the information about the site configuration? You can copy the information from Site Health.