502 Bad Gateway

Good afternoon. I did not wait for a response to my previous message. A new and more serious problem has appeared. After installing the plugin on the site, the site periodically has a 502 Bad Gateway error. After refreshing the page, the error disappears. The following message comes from WordPress:
Hi!

Starting from version 5.2, WordPress can detect errors with plugins or themes on the site and send you similar messages automatically.

This time, WordPress found a bug with one of the plugins-Prime Slider.
To solve the problem, you will need the following information:

WordPress version 5.7
Current topic: Hello Elementary (version 2.3.1)
Problematic plugin: Main Slider (version 1.12.10)
PHP version 8.0.3

Error Details
===================================
An error with the E_ERROR type occurred on line 23 of the file /public_html/wp-content/plugins/bdthemes-prime-slider-lite/freemius/templates/forms/deactivation/retry-skip.php. Error message: Uncaught ValueError: Unknown format specifier "?" in /public_html/wp-content/plugins/bdthemes-prime-slider-lite/freemius/templates/forms/deactivation/retry-skip.php:23
Stack Trace:
#0 /public_html/wp-content/plugins/bdthemes-prime-slider-lite/freemius/templates/forms/deactivation/retry-skip.php(23): sprintf('\xD0\x92\xD0\xBE\xD0\xB7\xBc\xD0\xBE\xD0\xB6\xD0\xBD\xD0...', '_get_uninstall_reasons('long-term')
# 4 /public_html/wp-includes/class-wp-hook.php(292): Freemius->_add_deactivation_feedback_dialog_box(")
# 5 /public_html/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters(NULL, Array)
# 6 /public_html/wp-includes/plugin.php(484): WP_Hook->do_action(Array)
# 7 /public_html/wp-admin/admin-footer.php(78): do_action('admin_footer', ")
# 8 /public_html/wp-admin/plugins.php(782): require_once('/home/f / admin...')
#9 {home}
abandoned