The link you followed has expired.

Hi there,

can you try disabling any cache plugins first. If still an issue, disable all other plugins aside from GP Premium.

I disabled One Signal Plugin. Now it's working. Thanks

You're welcome

I had exactly same problem and solved by disabling One Signal Plugin, thanks! This problem occurred right after updating onesignal plugin to latest version. Only hooks were affected, I was able to update post and pages.

Yes, the same happens to me. I have 3 sites using GeneratePress Theme. I have used OneSignal in 2 sites and after updating the OneSignal to the latest version this issue occurs.
I think we need to contact OneSignal Team.

Hi there

This seems to be a common issue with them right now:

https://wordpress.org/support/topic/link-expired-cannot-log-into-wp-admin/
https://wordpress.org/support/topic/downgrade-from-latest-version/
https://wordpress.org/support/topic/link-expired-issue/
https://wordpress.org/support/topic/link-expired-problem/
https://wordpress.org/support/topic/link-expire/

Problem solved with new version 2.0.1 of Onesignal:

Bug fix: link expired issue due to failing nonce check when creating posts from other WordPress plugins

Glad they got it fixed :)