I have one web site that freezes for up to 15 minutes saying "no internet connection".
Not noticed it on other sites,could it be an issue with just this one?It does come back to life and works fine again.
Have you cleared your cache? Settings->Safari->Clear History and Website Data
If you go to the same site with a computer, does it have a popup? Perhaps the Block Popup settings is making this happen. Settings->Safari->Block Pop-ups, turn it off. If this does not fix it, turn it back on.
Are you running an ad blocker in Safari? I find that mine occasionally interferes with a site here and there and need to disable it to get on the site. Settings->Safari->Content Blockers, turn it off. If this does not fix it, turn it back on.