When i'm using proxies i sometimes i got timeout error

I'm trying to scrape toysrus.com. Also i build scrapy spider for it and the problem is next:

It is work perfect without proxy. It scrape 100% pages and very fast. When i'm trying to scrape through proxy(crawlera) through time(a couple of times successfully and couple vice versa) it raise timeout(at all works not stable) and i don't know what to do with this. I'm using next headers:

'Host': 'www.toysrus.com',
'Connection': 'keep-alive',
'Proxy-Connection': 'keep-alive',
'Pragma': 'no-cache',
'Cache-Control': 'no-cache',
'User-Agent': 'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.86 Safari/537.36',
'DNT': '1',
'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
'Accept-Encoding': 'gzip, deflate, br',
'Accept-Language': 'en-US,en;q=0.8',
'Upgrade-Insecure-Requests': '1',
'X-Requested-With': 'XMLHttpRequest',
'Referer': 'https://www.toysrus.com/',

If it needs i can provide api key(maybe you can look at logs).
Can you help me?