I'm afraid, there are several templates which are modified and there is a lot of custom CSS. Google Analytics and Facebook Pixel have integrations in our software so should not be injected into the templates to make life simpler for yourself.
Keep in mind that any modification to a template would cause it not to be automatically upgraded so our software does not wipe out your modifications. Thus, the template would be outdated and therefore not be compatible with the latest release and cause your issue. You would need to ensure that your modified templates are compatible to reduce issues.
However, before we even go down that road. As mentioned, you would need to switch to an unmodified theme to test the issue at hand here is with your theme or not. If you do not want to do that, I'm afraid, we are beyond the extent of support which we can offer you. As we do not support custom theme development so would not be able to inform you on how to correct that.
It is worth noting that if it has been 2 years since your last upgrade, your modified templates are horribly out of date. Thus, you would want to switch to an unmodified theme to see if it is the out of date theme or not causing the issue.
You also want to disable any third party add-on to ensure outdated add-ons aren't influencing the outcome of your UI.