Messages windows won't open from tray

after installation eM client nevertheless v.8 or v.9 I can open/reply one or two mails. After that all reply windows appear and sit in tray, no way to open it!
What I’m doing wrong?
Windows 10 Pro (20H2)

The window may be off screen.

Hover your mouse over the taskbar icon. When the thumbnail appears, right-click in the thumbnail and choose Move. Use the keyboard arrow keys to bring it back on-screen.