I cannot believe it, my Gmail account is blocked again. This afternoon I decided to download the remaining messages to my mail client. I only had a few months left to download and estimated that the amount would be less than what I downloaded 2 days ago, so I should be safe. But no, ten minutes ago I received the lockdown message again. Luckily I now have almost all my messages downloaded (it stopped on Dec. 24, so one week left), and so I have a back-up of most mails. I will send Google an email once again, but am afraid it does not make any difference. I only received an automated reply to the mail I sent them two days ago, so I wonder if anybody is actually looking into this.
So a warning to all of you: if you use Gmail do not download all messages at once to a new email client. At least not when you have so many emails in there as I do: over 12,000 business and private emails in about 8 months of Gmail usage (I delete all spam and non-important mails), in total about 1.6 GB of information. Will keep you posted when they decide to let me use it again. Thanks Google 🙁
Update: Gmail started working again after about 20 hours.