Hi,
So, I've looked deeper into it, and I've seen two issues:
First, there was a bug which generated a JS error in some cases. I've made a patch and updated HikaAuction on your website for this. Before the patch, I was able to reproduce the issue this morning once or twice, even though it worked most of the time. Once I added the patch, I was not able to reproduce the issue anymore. Note that the patch requires you to clear your browser's cache (hard refresh).
Second, there are problems with the CORS policy of your website.
It prevents my browsers from loading the proper JS / fonts. See some of the error messages in the console of my browser:
....
13:14:01.467 www.xxx.com/media/mod_gptranslate/js/jsonrepair/index.js?e7eb31:1 Failed to load resource: net::ERR_FAILED
13:14:01.467 template-default-test:1 Access to script at 'https://www.xxx.com/media/system/js/messages.min.js?9a4811' (redirected from 'https://cdn.xxx.com/media/system/js/messages.min.js?9a4811') from origin 'https://xxx.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
13:14:01.467 www.xxx.com/media/system/js/messages.min.js?9a4811:1 Failed to load resource: net::ERR_FAILED
13:14:01.468 template-default-test:1 Access to script at 'https://www.xxx.com/media/com_finder/js/finder.min.js?755761' (redirected from 'https://cdn.xxx.com/media/com_finder/js/finder.min.js?755761') from origin 'https://xxx.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
13:14:01.468 www.xxx.com/media/com_finder/js/finder.min.js?755761:1 Failed to load resource: net::ERR_FAILED
13:14:01.468 template-default-test:1 Access to script at 'https://www.xxx.com/media/system/js/keepalive.min.js?08e025' (redirected from 'https://cdn.xxx.com/media/system/js/keepalive.min.js?08e025') from origin 'https://xxx.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
13:14:01.468 www.xxx.com/media/system/js/keepalive.min.js?08e025:1 Failed to load resource: net::ERR_FAILED
13:14:02.481 fa-solid-900.woff2:1 Failed to load resource: net::ERR_FAILED
13:14:02.481 template-default-test:1 Access to font at 'https://www.xxx.com/templates/flex/fonts/Pe-icon-7-stroke.woff?d7yf1v' from origin 'https://xxx.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
13:14:02.481 Pe-icon-7-stroke.woff?d7yf1v:1 Failed to load resource: net::ERR_FAILED
13:14:02.504 template-default-test:1 Access to font at 'https://www.xxx.com/templates/flex/fonts/fa-brands-400.woff2' from origin 'https://xxx.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
13:14:02.504 fa-brands-400.woff2:1 Failed to load resource: net::ERR_FAILED
13:14:02.527 template-default-test:1 Access to font at 'https://www.xxx.com/templates/flex/fonts/Pe-icon-7-stroke.ttf?d7yf1v' from origin 'https://xxx.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
13:14:02.527 Pe-icon-7-stroke.ttf?d7yf1v:1 Failed to load resource: net::ERR_FAILED
I'm surprised you don't have the issue with fontawesome on your website. I tried on Chrome, Firefox and Opera and had the issue on all of them.
I would recommend looking into the CORS policy of your website.