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Thanks OG. Yes, most definitely the same router. Router name began "ABC" with a simple suffix word. Neither of us had been to the place before and had no connections with the company. In fact, I only learnt later that the boatyard name was a trading name with the real company behind it called "ABC xxxxxxx". I'm not familiar with null passwords so I don't know. He did try to connect but failed - his phone continued to ask for the password.
It's very odd and I've not heard of anything like this before.