OK, that’s fine. More than happy to try anything from the comfort of indoors 
I’m absolutely certain now that the overrun only happens during disconnect/reconnect due to WiFi dropout so the latency would more likely be due to time spent reestablishing the connection - although I agree logging in the callback looks like a bad idea as it will only compound the effect.
I say this because my latest debug setup is showing me that the overruns are always happening after disconnection/reconnection.
As a general approach, would it be sensible to call hardware.sampler.stop(); then hardware.sampler.start(); when an overrun is reported by the callback?