Error 054: I will let you know if it happens in Test (since I am getting (History) data in Test); and if it causes a problem in Trade.
1. Not sure what 15 mins has to do with EOD data.
Yes, I have seen the Alpaca adjust start date messages.
2. I saw request for, say, 2016 to today (2021) all successfully downloaded, followed by a request for 2016 to (sometime in) 2017, also successfully downloaded. Not sure why - seems a waste of bandwidth. But from what you say it's Zorro's issue, not yours.
3. Yes, this is what I see; except "couple of more" seems to vary from 2 to 5+ tries - no idea why, but also Zorro's issue.