wcj_download_tcpdf_fonts_hook seems to be causing problems when cron runs

I have been trying to track down a warning in my log files.

These warnings fire every time your hook wcj_download_tcpdf_fonts_hook fires in the wp-cron tasks.

Warning: Cannot modify header information – headers already sent by (output started at /home/nzin2020/dev.nzin2020.nz/wp-cron.php:28) in /home/nzin2020/dev.nzin2020.nz/wp-content/plugins/wpfront-notification-bar/classes/class-wpfront-notification-bar.php on line 63

Warning: Cannot modify header information – headers already sent by (output started at /home/nzin2020/dev.nzin2020.nz/wp-cron.php:28) in /home/nzin2020/dev.nzin2020.nz/wp-content/plugins/google-apps-login/core/core_google_apps_login.php on line 452

This warning does NOT appear other times the cron tasks run. As far as I can see. Just when your one runs.

I realise the line of connection is a bit sketchy. But I was hoping you might have any idea what’s causing this?

THanks