May I know if you have checked marketplace plugin with WooCommerce and standard theme (storefront/twenty). Please deactivate all your plugin, except WooCommerce and WCMp + addon. You can then check the flow. If everything is working fine, in order to detect which plugin is causing conflict- please activate each plugin consecutively and check the flow.
Similarly, for theme conflict- please deactivate the current theme and check with standard WooCommerce theme (storefront/twenty) It is suggested to please perform these tests on your staging website and keep us posted with the outcome.
TwentyTwenty theme do not have a sidebar so the vendor review is visible at the footer of the page as you can see here (https://prnt.sc/xpguz2).
Regrading Themify Ultra/Shoppe, kindly check if this theme has side bar or not as that is the reason why the vendor review is not visible on the sidebar. If you want to make it visible to the sidebar, kindly reach out to the theme developer for the same.