I wouldn't overthink this. It was annoying the pub let your 3 articles build up and posted all together, but if they were good stories, a one off thing like that shouldn't turn your subscribers off. Consistency is important but unfortunately we don't have control over publications schedules and I've found there can be long gaps in submitting to a pub and it being published, even if self published. I am.sure your subscribers won't think you are spamming because they got 3 articles at once and this story explains why anyway. So they will appreciate your honesty and conscientious approach more, if anything.