1/ Download XStore – Installable Archive from this page – https://www.8theme.com/downloads/ and re-upload theme files, do the case for the XStore Core plugin.
Clear cache and check if the page can be edited.
2/ Try to disable all the third-party plugins (including cache plugins), that do not come bundled with XStore https://xstore.helpscoutdocs.com/article/36-included-plugins , clear cache of browser, then check. Maybe one of the additional plugins is a reason for the problem.
Let us know the results.
One standard license is valid only for 1 project. Running multiple projects on a single license is a copyright violation.