All plugins are always getting an error : Update failed: -1 when updating them

Disable and delete the Astra Starter Templates plugin. That’s known to cause this problem.

It seems that merely disabling the Astra Starter Templates plugin worked for me – I did not need to delete it.

@markfarrar: Sure, but what’s the point in having a plugin that’s deactivated, and just sits there and does nothing?

The problem with the plugin has been fixed in the new version. But if you simply re-activate the version on your site now, the problem returns and you can’t update to the new version. So you need to completely delete the current version… before you can install the new, problem-free version.

But do you even need the plugin at all? No, you don’t.

This plugin, as the name suggests, merely downloads the Astra Stater template so you can customize it. Once it does its job of downloading the starter template, it serves absolutely no purpose again — unless you want to use it to download another starter template and re-do your site from scratch.