Support

Hello,

can you please attach the log of the failed backup? So I can take a look at what's going on during the backup process.

Yes, that was what I was afraid of.
Your host is imposing very low limits on CPU usage: if you exceeding them, you get temporary blocked.
Now, let's start to tweak your configuration to optimize everything. Please try these suggestions one by one, if they work, there's no need to apply the next one. That's because every change will make your backup process slower (so it will require fewer resources), but let's try to avoid making it dead slow.

1. Exclude folders wp-content/uploads/cache and wp-content/cache from the backup. Looking at the logs, there's only temporary data, which we can safely ignore.
2. Double check that the Site Engine Scanner is set to Large site scanner
3. Inside the Archiver Engine settings, set the Part size option to 20Mb
4. Use the following timing settings: Minimum execution time 5 seconds, Maximum execution time 3 seconds, Runtime bias 50%. Yes, minimum is greater that maximum, that's not a typo.

Give it a try and tell me if those suggestions did work for you.

I was writing this while your new answer was posted:
Yes sure, you can ask your host to take a look at it. Usually hosting companies aren't very inclined to perform changes, but I glad to see there's an exception from time to time!
However, I'd strongly suggest you to apply the first 2 points of my bullets list: you really don't need to save cache data (it will only take space and time since it will be generated again form scratch) and you should double check that the scanner is the correct one, since it will speed up the whole backup process.

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Please try to lower the execution time AND to contact your host. It seems they are banning the user that's requesting the same page too many times in a small timeframe, usually it's a security setting to prevent DOS attacks.

If you're Ok with that, I'll make this ticket public, so it could help other people struggling with the same problem.
And yes, it's always a good thing to avoid updating/backing up all the sites at the same time, since you could hit resource usage limits. I had the same exact problem with RAM usages.