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At the moment when I check the Bootstrap code, I found it may be due to some Boostrap online link has outdated.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.
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.