As Fugi says, never rely on JOIN/PART. Let alone at channels of above 1000 chatters, JOIN/PART are not emitted anyway. So do not rely on them, ever.
JOIN/PART has always been this way…
Sure there are valid reasons for knowing who is or is not in a channel, but I have never relied on JOIN/PART myself as it’s never been “reliable”
On the subject of Chatty, even that userlist will not work for channels post 1000 users, and Twitch doesn’t have to help or support third party programs.
@MikeyDK the end point that @trumpi27 mentions works all the time regardless of the channel online/offline status. I follow what @trumpi27 does and ignore bad responses and smooth accordingly…
On the subject of Mod status, as @MattiSony says issue /mods and parse the NOTICE response, you will need the COMMANDS CAP for this.
If you are suppling the main bot for the channel on a 1 on 1 level, it should be fairly safe to assume the bot is modded, since surely you will have put in a shutdown command or additional ways for the channel owner to control/stop/restart the bot so the issue of “is the bot modded” is not a issue (personally speaking)