A.P. Shkardun

The solution: Duplicate the imported form and use a copy. The channels will appear all right.

No, I imported only the forms and then submitted messages through them.
This is how it looks: https://testfront.typingcommander.com/wp-content/uploads/2021/09/Flamingo_inbound_messages.png
The three messages were submitted through the imported forms, the last message was submitted through the preinstalled form “Contact form 1”.
The drop-down list “View all channels” appeared only after submitting the last message.

The version 2.8.2 has fixed this.
Thank you.

I’ve checked the source code and have not found any mistakes.
Can anybody point at the mistakes in the source code?
Or maybe the mistakes lie outside the source code?

Actually v2.6.1 does not use Font Awesome, at least in /wp-content/plugins/elementor/assets/css/frontend.min.css.
It uses eicons instead (at least in that css file).
So, the solution is to use this css code to roll back to Font Awesome:

.elementor-slick-slider .slick-prev::before {
    content: "\f104" !important; /* the initial value was "\e89f" */
}

.elementor-slick-slider .slick-next::before {
    content: "\f105" !important; /* the initial value was "\e89e" */
}

.elementor-slick-slider .slick-next::before,
.elementor-slick-slider .slick-prev::before {
    font-family: FontAwesome !important; /* the initial value was eicons */
}

Or to wait until Elementor’s team will fix eicons.

Upgraded to 2.6.1
The problems are still there.

is there a way to view all reported posts from the Dashboard rather than being notified by email. My email would be flooded.

I agree.
For example, the plugin bbPress – Report Content creates two separate lists of 1) reported replies and 2) reported topics accordingly on the back-end. I would recommend the author to look closely at that plugin and, maybe, even take the appropriate code from there.
On the other hand, this plugin allows to select a reason for reporting, which bbPress – Report Content does not.