Hi Chris,
On the one hand, I hope that the link provided by Alexey was helpful to you. On the other hand, quite often I also see 'connection timeout' warning in my tests and I think that this is something that may be discussed on some LoadComplete class that I mentioned here: https://community.smartbear.com/t5/LoadComplete/Clear-Explanation-of-Scenario-Completion-Time/m-p/137466#M1505.
In my case, these warnings are also a kind of 'sporadic ones'. I.e., considering some given test as a n example, the test runs fine for, say, 5 virtual users (VUs). But when running, say, for 15 VUs, it may pass or fail with the mentioned warnings on a random basis. At the moment I can think about two possible reasons for this:
a) There is some bottleneck on the way. It is my understanding that in this case you should examine your network and server logs to check that something (network, server CPU, memory, database server, etc.) is not congested so that this congestion causes connection timeout;
b) It was mentioned by Support in some other thread here that connection timeout or response status 500 might be an indication of server overload (i.e. you got your server's capacity limit). Again, this should be checked on the server side.
Unfortunately, I did not have access to the server side in my cases, so everything from above is just my current theoretical understanding that might or might not appear to be correct. This is another reason of why I would appreciate the relevant class from SmartBear. :)
P.S. I believe that I will be corrected in case I wrote something incorrect here...