Discord JDA - Sometimes working, sometimes not - discord

Question

What i am trying to do is :
When a guy leave a specific voicechannel, and this channel is now empty, the bot :
delete all the messages but 1 in a specific textchannel
delete the voicechannel he just left
The problem :
the voicechannel is successfully delete, but the messages in the textchannel are not delete by the bot
The code :
#Override
public void onGuildVoiceUpdate(GuildVoiceUpdateEvent event) {
VoiceChannel channelLeft = event.getChannelLeft();
if (channelLeft.getName().startsWith("🎒 Coaching de")) {
if (channelLeft.getMembers().isEmpty()) {
channelLeft.delete().queue(); //The bot delete de channel successfully
List<Message> messagesCoaching = event.getChannelLeft().getGuild().getTextChannelById("489420943991635988").getHistory().retrievePast(20).complete(); // Using a list to store the retrieved messages
messagesCoaching.removeIf(m -> m.getId().equals("490567304971812885")); // Removing from the list the message i want to keep
event.getChannelLeft().getGuild().getTextChannelById("489420943991635988").deleteMessages(messagesCoaching).complete(); // Deleting all the messages (not working)
}
}

Answer 1

I'm not 100% sure what your error is, but I'll assure you're trying to delete all messages sent in the text channel.
Currently, your code gets the last 20 messages from the text channel that you got by an ID. If you have more then 20 messages, the bot won't delete those. And if the messages are older then 2 weeks, it won't delete them either. Furthermore do not use complete() as this will stop the main thread of the bot. I'd suggest using code like this:
#Override
public void onGuildVoiceUpdate(GuildVoiceUpdateEvent event) {
VoiceChannel channelLeft = event.getChannelLeft();
if (channelLeft.getName().startsWith("🎒 Coaching de")) {
if (channelLeft.getMembers().isEmpty()) {
channelLeft.delete().queue(); // Telling the bot to delete the channel.
MessageHistory history = event.getGuild().getTextChannelById("489420943991635988").getHistory(); // Pulling up the history from a text channel
history.retrievePast(100).queue(messages -> { // Putting the past 100 messages in a queue, and using a lamba to do something with the returned messages
messages.removeIf(m -> m.getId().equals("490567304971812885")); // If a message contains the same ID as told here, it removes it.
event.getGuild().getTextChannelById("489420943991635988").deleteMessages(messages).queue(); // And now, delete all messages.
});
}
}
}