Hello,
1) What version of the XStotre theme did you use before? What version of XStore Core plugin do you use? Have you also updated it to latest version 1.2.4?
2) What version of WPBakery page builder do you use?
3) Have you set the portfolio page in Theme Options > Portfolio > Portfolio page?
4) If all the plugins are up to date but you still have the error then provide me WP Dashboard and FTP access to check problem in more details.
5) What error do you get while trying to create the new topic https://gyazo.com/a600dce89e26e20d84e54cb40f148e9d ?
Regards