Hormones are so weird, aren't they? That syncing thing makes no sense but has happened to me too with my good friend. When we hang out, we always have our lady friend at the same time. Then when we have periods where we are both too busy to get together, it separates back out and then when we reconnect and start walking and doing things together again, right back to being on the same cycle pattern. weird. So, you never know. You could be having a hormonal blip and I just wouldn't worry about this.