Oh I see what you mean. There's no reason an alert wouldn't be triggered unless it's not meeting the conditions to trigger again (eg, the thread hasn't been read since the last alert). The same conditions are used for watch thread emails. It is a false assumption that alerts actually "alert" you every time someone replies to a watched thread. So you get one alert - for the very next reply after you've read the thread - and then you don't get any more, regardless of how many more people reply to it, until you read it again. Otherwise, you could end up with hundreds of alerts. This is intentional, pushing single alerts for one thread when you ignored the first alert aside from "quoted you/reacted to your post" is superfluous and vexatious. The system respects your decision for not visiting the thread after you get an alert and ignored it and will stop pushing alerts until you visit the thread again.
Hope that helps.
