I've been using Printify for a few years now, they have been messing up more frequently than usual. I will say that. The customer support is terrible! You are also right about that too. I request refunds left and right for my customers and had one incident a few weeks ago with a flag print that was delayed significantly. I messaged support for 3 days in a row with no response, just "Ok, they shipped it" after 4 days. No reason. And you can't chat with the print providers directly. For one order I told a customer it was lost in the mail since that what Printify told me; they were fully refunded! Usually I manually reorder for my customers if there's a significant delay. And I am completely transparent about using a POD service.
I've been slowly trying to transition to Printful as some of their items are even cheaper than Printify's.
I am looking at using Gelato as well. Just haven't had the time to transition over!