Here’s a workaround that I found:
1. Rename the “wps-hide-login” folder via FTP/CPanel, which will force the plugin to deactivate.
2. Log in to wp-admin like you would normally.
3. Go to your wp-admin > Settings > Permalinks page.
4. Click “Save Changes”. Wait for the page to refresh.
5. Click “Save Changes” again. Wait for the page to refresh again.
6. Change the plugin’s folder name back to “wp-hide-login”.
7. Reactivate the plugin via the Plugins page.
WordPress has a lot of random issues that can be fixed using this method, so I’m not sure if this is a problem with the plugin itself or something involving WordPress’s core.