Thanks @Ryan_Miles I saw these in the event log that support your statement:
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However the sensor can see four APs that are all MR42s running 28.4 and one of them has a -67dBm signal
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So far I've tried rebooting the MT, multiple of the MRs, making sure Bluetooth is on and am now a bit stuck!
If my answer solves your problem please click Accept as Solution so others can benefit from it.