Why does Opencart 2.3.0.2 (rs.6) give "A theme has not been assigned to this store!"?

Question

opencart

Good day!
Something strange happened. There is a store on Opencart 2.3.0.2 (rs.6), went to Modules->Themes and changed the size of product images.
After that, the site began to issue "A theme has not been assigned to this store!" + other themes are not visible in the settings, only the standard template, although the directory is displayed in Modules-> Themes.