An update with the Starter Templates caused a nonce issue not allowing plugins to update on your website. In some cases, resulting the site to go into maintenance mode.
This issue was immediately resolved in a hotfix released in version 3.1.26 of the Starter Templates/Premium Starter Templates plugin.
You can simply follow these steps to resolve the issue if you are below version 3.1.26:
Step 1: Please deactivate our Starter Templates plugin and update it to the latest version.
Step 2: In the meantime, Update other plugins that have pending updates and there shouldn’t be an issue with updates
Step 3: Reactivate the Starter Templates plugin as all the plugins are resolved and with Starter Templates updated to the latest version.
Note: In rare cases, if the above steps do not help. You can deactivate and delete the plugin temporarily and install the latest version from the Starter Templates plugins page or My Downloads page for the Premium Starter Templates plugin.