This is Lana from Shopify. Sorry to hear that this issue is impacting your business.
From what you're saying here, it is possible that this issue is related to the cache and cookies on your browser. Have you tried saving those items on across various browsers/devices to see if it works? If not, try to clear your cache on the Google Chrome browser following these steps, then go back and see if it lets you make your changes.
If this does not work for you, could you tell me a little bit more about the specific errors that you're seeing? If you can attach a screenshot to show an example, that would be very helpful also!
Let me know if you have any other questions here and I will be happy to help.
I cleared my cache and cookies, it was also happening when my husband also tried on a different computer. It didn't matter what we were using when we saved it wouldn't save, just kept spinning like it would time out. We tried multiple times and eventually got the server error. I have fiber and have no issues with any other service, connection. It was the first time we had issues so for now just been leaving it alone and hoping it was just the server itself was busy and perhaps being updated.
It looks like you have done a lot of troubleshooting for this already! The next step I recommend is to contact our live support here so that we can take a closer look at this for you. The reason for having to contact us through there is because we are currently unable to access the account and investigate the issue from the Shopify Community.