Getting partial download errors on my credit union accounts

Since 2 days ago I've been getting Partial Download (-28) WITH FI_TIMEOUT:102 when I try to update my 3 accounts at SecurityPlus Federal Credit Union (checking, share, and money market accounts). 2 days ago I was getting errors trying to use those accounts in my browser outside of Quicken for Mac, which was just updated today to version 5.18.2, but that didn't help. Those errors in my SecurityPlus browser session said that my accounts had not finished updating, but as of 2 days ago, those "not finished updating" errors went away — but now I can't get Quicken to download my most recent transactions at SecurityPlus. The last SecurityPlus transactions Quicken successfully downloaded were "partial" downloaded on 9/28/2020. But on that same download attempt, I started getting the errors mentioned above.

Those errors keep happening now every time I try to do a Quicken download. Quicken is able to successfully download my transactions from my PayPal account and my BankAmericard VISA Platinum Plus account. It's just the SecurityPlus accounts that are not working. Using "Retry" doesn't help. Using the Quicken app on my iPad now reports "connectivity errors" on those same 3 SecurityPlus accounts.

I have tried to add my 3 problem accounts into Quicken again, using Action = "Link" for each, but the Account Status error window still keeps appearing with the same details shown.

Is there something I can do in Quicken to get past these problems? Is it possible that my credit union has changed (to my detriment) its way of honoring Quicken update attempts? In short, what must I do to get things back to normal, like they were working ever since the beginning of 2020? Thanks.