I also experienced the same issue. I disabled every extension including opera built-in ads block. I also experienced this on Opera on 2 platform windows and linux, both were latest version.
Chrome browser did not have this problem.
When I open dev tools to check for errors, I have this:
Refused to load the script 'https://payments.google.com/payments/v4/js/integrator.js?ss=m2' because it violates the following Content Security Policy directive: "script-src 'unsafe-inline' 'self' 'unsafe-eval' https://apis.google.com https://ssl.gstatic.com https://www.google.com https://www.gstatic.com https://www.google-analytics.com https://www.googleapis.com/appsmarket/v2/installedApps/". Note that 'script-src-elem' was not explicitly set, so 'script-src' is used as a fallback. m=_b,_tp:391 WARNING! m=_b,_tp:391 Using this console may allow attackers to impersonate you and steal your information using an attack called Self-XSS.Do not enter or paste code that you do not understand.
Hope this helps,