PHP errors in Total Upkeep Premium caused by Total Upkeep 1.17.3 and 1.17.4 #637

I am running Total Upkeep with the Premium extension version 1.5.13 (current stable) on WordPress 7.0.2.
After updating the main Total Upkeep plugin to 1.17.3, the WordPress admin immediately started showing these errors:

Warning: Undefined array key "icon_warning" in /wp-content/plugins/boldgrid-backup-premium/admin/class-boldgrid-backup-premium-admin-historical.php on line 546

Warning: Cannot modify header information - headers already sent by (output started at .../class-boldgrid-backup-premium-admin-historical.php:546) in /wp-includes/functions.php on line 7220

Warning: Cannot modify header information - headers already sent by (output started at .../class-boldgrid-backup-premium-admin-historical.php:546) in /wp-admin/admin-header.php on line 14

(and additional “headers already sent” warnings)
A new file was also created that did not previously exist:

/wp-content/.boldgrid-backup-locator.php

I also tested the main plugin version 1.17.4 — it produced different translation-loading notices and the same “headers already sent” cascade.

Current working state:
When I revert the main Total Upkeep plugin to version 1.17.2 and keep Premium 1.5.13 active, the errors disappear completely.
So the combination of Premium 1.5.13 + main plugin 1.17.3 (or 1.17.4) is broken. Premium 1.5.13 + main plugin 1.17.2 works.
Please investigate. I can provide PHP version, Site Health data, or any other details you need.

Thank you.