I noticed strange thing when a website is accessed in offline mode (router is switched off) the browser somehow remembers this, and after switching on the router and waiting few seconds for online, I'm able to open any other websites not accessed in offline mode, but when I try to open the first one (that I've tried in offline mode) I have to wait few minutes, and after that I receive an error message, even if I am online for sure.
Any ideas? Is it a bug?
it sounds like it has to do with loading from your cache.cache settings in system may influence this as well. i would recommend wget for webpages you want to keep offline. extensions like evernote (i use vivaldi version often) may be better for that purpose depending on what you use them for.