Yeasterday I found one of my websites became very slow and I tried many way but can't find a solution. At the moment when I check the Bootstrap code, I found it may be due to some Boostrap online link has outdated. And finally I found the link below was not available any more. I replaced this link and fix the problem.
https://cdn.jsdelivr.net/npm/bootstrap-icons@1.5.0/font/bootstrap-icons.css?ver=5.9.3
Sometimes, we use CDN source to save our development period, but we must be caution is the CDN source is stable. Some CDN source may become offline some day. As a consequence, your site would also become slower.