cc-502 errors and Pennsylvania State Employees Credit Union

Off and on over the past year I have had problems downloading transactions via express web connect from the Pennysylvania State Employees Credit Union. For most of the fall 2018 I was unable to download any transactions. By late winter, the problem seemed to be resolved. Then started up again in the Spring 2019; resolved by summer 2019, and more recently started in September 2019 again. If I disconnect all the accounts from PSECU and reconnect it sometimes works. (Unfortunately when I do that, it downloads about 3 months of transactions which I painfully have to go through item by item to delete until I get to the ones that are new.) None of my other accounts from Schwab, citibank, etc. have any problems. Oddly, I maintain my mother's financial accounts using the same version of Quicken 2017 (windows) on the same computer. When I do a one-step update via express web connect to download transactions from the PA State Employees Credit Union, I've never had any problems. PSECU and Quicken support seem to be of little help.