Is it possible you have a race condition between whatever is updating field 3 and the rest? If they both try to update within the same 15 second window then only the first one will succeed. Lately it looks like field 3 is winning more often than not.
https://api.thingspeak.com/channels/125785/fields/1.csv?results=10
2016-07-04 05:03:02 UTC,6201,
2016-07-04 05:04:02 UTC,6202,
2016-07-04 05:05:02 UTC,6203,127
2016-07-04 05:06:03 UTC,6204,
2016-07-04 05:07:03 UTC,6205,
2016-07-04 05:08:04 UTC,6206,
2016-07-04 05:09:04 UTC,6207,
2016-07-04 05:10:01 UTC,6208,135
2016-07-04 05:11:05 UTC,6209,
2016-07-04 05:12:05 UTC,6210,
https://api.thingspeak.com/channels/125785/fields/3.csv?results=10
2016-07-04 05:03:02 UTC,6201,47.078
2016-07-04 05:04:02 UTC,6202,47.615
2016-07-04 05:05:02 UTC,6203,
2016-07-04 05:06:03 UTC,6204,47.078
2016-07-04 05:07:03 UTC,6205,46.54
2016-07-04 05:08:04 UTC,6206,47.615
2016-07-04 05:09:04 UTC,6207,46.54
2016-07-04 05:10:01 UTC,6208,
2016-07-04 05:11:05 UTC,6209,47.615
2016-07-04 05:12:05 UTC,6210,48.154