I switched from Google Domains to Namecheap and found that they have a non-standard requirement for A records (they require an "@" A record) that messed up the transfer. Godaddy, dyndns, and Google Domains use regular zone transfer tables and I thought those entries were all I needed. Nope. I finally emailed support and they told me what was wrong within 24 hours. But meanwhile, my site was down for that time.

I suppose if you worked with one of the companies they partner with and use the automated templates to generate a new entry, it would work out fine. But I was transferring an existing domain. I know better now. But I put this out to warn others.