Shamim's Plugins

You can try a transparent loader. Add following code in Dashboard > Front End PM PRO > Settings > Appearance > Custom CSS

.fep-loader {
	-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=0)";
	filter: alpha(opacity=0);
	opacity: 0;
}

Please note loader will be transparent from all places for this in this plugin.

After sending message it should make an api call to get messages and load messages. So it should not be in grey stage for long time.
Can you record your screen when sending message so that i can see in which stage the issue is?

Message with more than 5 recipients, emails will be sent using cron. Can you check if your cron working properly? You can use any cron plugin for that (eg. WP crontrol)

Also can you please go to Dashboard > Front End PM PRO > Settings > Emails > Email Sending Interval and change to any other value and save changes. Wait selected amount of time and check again.
Let me know.

Sorry for delayed responses.
This plugin is not abandoned.
Hope i will be able to provide support regularly as before from now on.

Can you provide me your website url where you are trying to add the license?

This plugin do not use email address but username. So may be your other plugin use email address to generate username. They remove @ symbol when they create username.

Can you give me a screenshot where you are checking and what error you are getting?

By default only admin can send announcements. If you want any other role to allow please follow https://www.shamimsplugins.com/support/topic/create-announcements/#post-26559

You can use fep_action_message_after_send hook to save message id in database.
You can find some examples in https://www.shamimsplugins.com/support/search/fep_action_message_after_send/