Ionic v4 Page Not Available Error when hosting it as a website

so I build web app with ionic v4 angular (tabs style) recently. the problem is that i m constantly getting the “webpage not available” error randomly when I try to access my site on the server end. It happen very frequently on the mobile phone browser. I would say it happen 1 out of 10 hit/refresh. does any body have any idea what went wrong? btw, it seems to happen more on Android browser.

I tried to start a brand new project with “ionic start myApp tabs” and I got the same error. the only thing i changed were to use HashLocationStrategy and change the < base href="/" > to < base href="./" > in index.html to fix the refreshing page not found issue. I have been researching on this issue for days and found no answer. If any one know what the problem is, please let me know. thanks in advance.