Genericons appear square unless logged on as admin

My site does not show any Genericons with Full Frame Pro 4.1 unless I logged on as admin. Those icons provided by Font Awesome 6.1.1 look fine. Cache cleaning / theme-reinstallation / plugin-disabling & reinstallation all did not work. All icons look fine with Cocoon. Any suggestions are highly welcome. Thank you! Environment: PHP/7.4.28, Nginx/1.21.6, WordPress 5.9.3