PHP Uncaught Error in 2.7.0

The following appeared many times in my site root error_log when I had DEBUG enabled.
Using:
WordPress 5.5.1
Storefront 2.7.0
WooCommerce 4.5.1
PHP 7.4

[08-Sep-2020 17:33:01 UTC] PHP Fatal error: Uncaught Error: [] operator not supported for strings in /home/xxxxxxxx/bookings2.in-rhythm.com/wp/wp-content/themes/storefront/inc/class-storefront.php:447
Stack trace:
#0 /home/xxxxxxxx/bookings2.in-rhythm.com/wp/wp-includes/class-wp-hook.php(289): Storefront->body_classes(‘Array role-admi…’)
#1 /home/xxxxxxxx/bookings2.in-rhythm.com/wp/wp-includes/plugin.php(206): WP_Hook->apply_filters(‘Array role-admi…’, Array)
#2 /home/xxxxxxxx/bookings2.in-rhythm.com/wp/wp-includes/post-template.php(836): apply_filters(‘body_class’, Array, Array)
#3 /home/xxxxxxxx/bookings2.in-rhythm.com/wp/wp-includes/post-template.php(595): get_body_class(Array)
#4 /home/xxxxxxxx/bookings2.in-rhythm.com/wp/wp-content/themes/storefront/header.php(21): body_class()
#5 /home/xxxxxxxx/bookings2.in-rhythm.com/wp/wp-includes/template.php(730): require_once(‘/home/xxxxxxxx/…’)
#6 /home/xxxxxxxx/bookings2.in-rhythm.com/wp/wp-includes/template.php(676): load_template(‘/home/xxxxxxxx/…’, true, Array)
#7 /home/xxxxxxxx/bookings2.in-rhyt in /home/xxxxxxxx/bookings2.in-rhythm.com/wp/wp-content/themes/storefront/inc/class-storefront.php on line 447

Is there an issue in the theme, or could this be caused by a conflict of some kind?

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