@David-TP Thanks for your reply. I've spent quite a bit of time on this. The problem seems to be with the channels the decos pick. 2.4Ghz channels are quite congested here - inc some hidden SSID...

The most recent firmware update seems to have caused the XE75 Pros in my network to be very unstable and perform poorly. Reverting to the M5s sorts the problem but utilising an XE75 as the main deco...