I agree with this review. The authors don’t respond to support requests and the plug-in is only marginally functional. We are also looking into a dispute with Paypal.
We have been working with our themes provider (Elegant Themes Divi) to troubleshoot this problem. Eventually, it was discovered that the issue is happening because Easy TOC is using its own smooth scrolling script, and this is interfering with built-in smooth scrolling with the theme sitewide.
They have suggested that I ask you if it is possible to disable smooth scrolling in the Easy TOC plugin. I believe this would resolve the issue. Would that be a simple fix?