@Byteguy I can run a signal strength test, but the APs cannot be moved. If the signal strength is low, why is it that most of the time there is no problem. Seems to be intermittant. APs are really not all that far apart. Will look at power level on each. I understand that having every AP on high power can sometimes interfere with the signals. Had recently done firmware upgrade on the controller and had to reconfigure the whole mesh.

Can suggest to marina management that they have a way to monitor power at each transformer.

  @Byteguy  I have exactly the same problem with one or two mesh access points, albeit they are not TP-Link heads (yet) but for 90%+ of the time they perform just fine in an external arena setting. However, occasionally one or both will lose connection for a short period but normally recover service without operator intervention.  This has been going on for a few years without much adverse comment. 

Originally I spent many hours trying to get to the root of the problem and eventually surmised that the signal linking the mesh units, whilst generally OK, could fluctuate under certain atmospheric conditions (weather & pressure) and lead to mesh drop-outs.

I, no longer worry about it - the situation seems to self-correct without issue.

  @GaelForce I think you're right. I visited with the marina manager and he wasn't aware of any power fluctuations, but no one has been complaining about their connectivity.

One reason the wireless signal may be getting messed up is due to the nature of the installation. It's a marina. Lots of masts getting in the way of the signal, especially when it's windy and the boats are moving around.

Guess I won't worry about it unless the controller goes offline. Now that would have to be a power problem, but I had the management get a good UPS for the system.