Certain Https sites no longer accessible for me with Ventura update (in Chrome and Safari)

Updated an iMac and MacBook Pro this week to Ventura. Now I can't login to certain websites I could log into before. Tried both Chrome Version 107.0.5304.87 and Safari 16.1. Chrome returns "This site can’t provide a secure connection.......... sent an invalid response.ERR_SSL_PROTOCOL_ERROR" and Safari returns "Safari can't open page..... because the server where the page is located isn't responding".

I've tried 2 different computers (both Ventura OS), 2 browsers, 2 different networks all with the same problem. Deleted cache, tried different users with admin access, tried safe mode, rebooted computers, rebooted network and no luck. It seems like it has to be some OS setting that is causing the problem, but I can't figure it out. I'm at a loss.