[Hummingbird] Hummingbird generates error in debug log

Unable to resolve debug error: "[02-Apr-2018 19:21:05 UTC] PHP Warning: Illegal string offset 'sow-hero-default-8f2bc4049114' in /data/19/2/35/75/2687075/user/2950978/htdocs/wp-content/plugins/wp-hummingbird/core/modules/minify/class-minify-group.php on line 416
[02-Apr-2018 19:21:05 UTC] PHP Warning: Illegal string offset 'sow-hero-default-8f2bc4049114' in /data/19/2/35/75/2687075/user/2950978/htdocs/wp-content/plugins/wp-hummingbird/core/modules/minify/class-minify-group.php on line 437
[02-Apr-2018 19:21:08 UTC] PHP Warning: Illegal string offset 'sow-hero-default-8f2bc4049114' in /data/19/2/35/75/2687075/user/2950978/htdocs/wp-content/plugins/wp-hummingbird/core/modules/minify/class-minify-group.php on line 416
[02-Apr-2018 19:21:08 UTC] PHP Warning: Illegal string offset 'sow-hero-default-8f2bc4049114' in /data/19/2/35/75/2687075/user/2950978/htdocs/wp-content/plugins/wp-hummingbird/core/modules/minify/class-minify-group.php on line 437
[02-Apr-2018 19:38:33 UTC] PHP Warning: Cannot modify header information - headers already sent by (output started at /data/19/2/35/75/2687075/user/2950978/htdocs/wp-admin/includes/file.php:1720) in /data/19/2/35/75/2687075/user/2950978/htdocs/wp-admin/includes/misc.php on line 1114"