Problem

When upgrading WordPress core, theme, language or plugin – the update downloads successfully but leaves a blank upgrade screen, the page stops loading, you may be stuck in maintenance mode (requiring manual removal of .maintenance) and overall the upgrade never completes.

Observations

1. Using WordPress version 4.x
2. Accessing the WordPress site via HTTP (not HTTPS)
3. When upgrading, I saw WordPress downloaded the zip file via HTTPS
4. Using WordPress.com Jetpack (not sure if related or not)
5. Google returns very few results describing the problem well.

Workaround

I’ve tested this against four WordPress sites now and it appears to have successfully worked around the problem.

I installed a self-signed SSL certificate against the WordPress site using Server Name Indicator (SNI). Remember no dedicated IP is required when using SNI but it need a compatible server. For convenience I’ve used SSL certificates from tinycert.org.

Now when I access the site over HTTPS:

1. Login again – note SSO with untrusted certificate will not work, you must use local site login credentials
2. Perform the upgrade – it completes successfully and does not result in a blank or stalled upgraded screen.

Do you see another pattern? Isolated it to a version, Jetpack or another update? Please let me know!

Other Possible Causes

The above resolved my issue, but similar issues include:

• WordPress running out of memory