Private proxies are the bomb for scraping, but you have to have a lot of them to do any serious scraping on google, or reduce your connections - and especially when scraping with advanced operators (inurl: etc).
You can take my word for it or not, but trust me i've been frustrated so many times just like you, been back and forward with scapebox support, and i can tell you that if im scraping google with 100 semi dedi proxies with advanced operators then il only scrape with 5 connections or in other words at a 20:1 ratio.
If im not using advanced operators i scrape at 8 or 10 connections, or a 10:1 ratio with 100 semi dedi proxies.
Your private proxies are burnt at the minute, you'll have to lay off scraping google with them for a day or a day and a half or so until google unban them. It's not that they're banned from scraping everything, or performing page rank checks or anything, but they are defo banned from scraping advanced operators.
Go to settings >> use multi threaded harvester - and uncheck this. Then try and harvest, there will be a status column. What errors are you getting in the status column?
Here is a video by loopline that goes over how to do this and other troubleshooting for the harvester that might be helpful, and will defo show you that some or most of your proxies are currently banned when you use the single thread url harverter.
https://www.youtube.com/watch?v=2QaLWgTXsRo
999 from yahoo means the IP is blocked. 302 from google means the IP is blocked. Are you scraping for advanced operators? If so this video by loopline will be helpful:
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> In general google has really cracked down lately on banning IPs much faster. There is no rhyme or reason to it either, proxies can pass the proxy test and then if you immediately retest them they can show failed.
Since google is such a bitch with their advanced operators, and since yahoo doesn't allow you to lose a lot of them but does allow you to scrape at a high number of connections, a good tip is to use a tool like "Footprint Factory" and scrape just a few say inurl: results and then analyze them with Footprint Factory. Then use the footprints that generates to scrape with in Yahoo.