I've just seen a POST /ajax/vrequest HTTP/1.1 that's supposed to load the timeout until the captcha and that was answered with a 403 from your server.
Don't you have any logs? I bet you find tons of 403 and 404 in there.
Or this one:
11:39:02.401193 [...] > 198.154.102.18.80: P [bad tcp cksum 5f97!] 2519:3176(657) ack 2497 win 16603 (DF) (ttl 127, id 57636, len 697)
[...]
GET /captcha?c=view&uid=[...] HTTP/1.1
Host: btcclicks.com
Connection: keep-alive
[...]
11:39:02.623465 198.154.102.18.80 > [...]: . [tcp sum ok] 2497:2497(0) ack 3176 win 172 (DF) (ttl 54, id 27013, len 40)
[...]
11:39:14.699238 198.154.102.18.80 > [...]: . 2497:3949(1452) ack 3176 win 172 (DF) (ttl 54, id 47128, len 1492)
[...]
HTTP/1.1 200 OK
[...]
12 seconds to load the captcha.
11:43:03.216432 [...] > 198.154.102.18.80: P [bad tcp cksum f3ee!] 1577:2267(690) ack 8451 win 16603 (DF) (ttl 127, id 8866, len 730)
[...]
GET /view?a=de62719500104a229d2106f835feeb03183fabb12ddbe46af1d409feab92f2ea HTTP/1.1
Host: btcclicks.com
Connection: keep-alive
[...]
11:43:03.399658 198.154.102.18.80 > [...]: . [tcp sum ok] 8451:8451(0) ack 2267 win 154 (DF)
[...]
11:43:03.436719 198.154.102.18.80 > [...]: . 8451:9903(1452) ack 2267 win 154 (DF) (ttl 54, id 49389, len 1492)
[...]
HTTP/1.1 404 Not Found
Server: nginx
Date: Sun, 07 Sep 2014 09:42:57 GMT
[...]
404 with timestamp from your server. (Your clock is off btw). The ad was not expired or anything. A reload worked fine.
And finally I managed to get "An error has occured" when solving the captcha. This didn't even cause any network traffic AFAICS.
I'm probably wasting 50% more time due to all these errors because I have to load ads over and over or solve captchas twice etc.
Not cool.