When you go to SOGo page via link which opens it in new tab:
https://demo.sogo.nu/SOGo/
you cannot delete opened message by Trash icon then.

I see warning in WebConsole:
DOMException: Blocked a frame with origin "https://demo.sogo.nu" from accessing a cross-origin frame.
at k (https://demo.sogo.nu/SOGo.woa/WebServerResources/js/Mailer.services.js?lm=1596200616:1:52733)
at e.deleteMessage (https://demo.sogo.nu/SOGo.woa/WebServerResources/js/Mailer.services.js?lm=1596200616:1:57920)
at fn (eval at compile (https://demo.sogo.nu/SOGo.woa/WebServerResources/js/vendor/angular.min.js:1:1), <anonymous>:4:181)
at e (https://demo.sogo.nu/SOGo.woa/WebServerResources/js/vendor/angular.min.js:198:191)
at m.$eval (https://demo.sogo.nu/SOGo.woa/WebServerResources/js/vendor/angular.min.js:154:468)
at m.$apply (https://demo.sogo.nu/SOGo.woa/WebServerResources/js/vendor/angular.min.js:155:198)
at HTMLButtonElement.<anonymous> (https://demo.sogo.nu/SOGo.woa/WebServerResources/js/vendor/angular.min.js:198:276)
at xg (https://demo.sogo.nu/SOGo.woa/WebServerResources/js/vendor/angular.min.js:40:394)
at HTMLButtonElement.d (https://demo.sogo.nu/SOGo.woa/WebServerResources/js/vendor/angular.min.js:40:341)

This problem has browser dependency.

• firefox in debian - works fine
• chromium in debian - cannot delete
• firefox in windows - cannot delete
• ms edge in windows - cannot delete

Other cases:

• page https://demo.sogo.nu/SOGo/ is opened by link in the same tab => works fine
• page https://demo.sogo.nu/SOGo/ is opened in new tab manually => works fine
• message is opened by "New Mail Window" icon => works fine
• message is marked in its check-box and deleted by "group" Trash icon => works fine