Ac one mini - maintenance mode or deliberate power down

Hi Folks,
I have 3 AC one mini’s in a 340m2 two storey wooden building, all carrying the same SSID’s, all configured with the same Trunk ports back to one router. Today I deliberately powered one down Ap, as its really only required when business functions are on and I needed the POE port it was using.
The result: the 2 Ap’s would not carry the connection on unless I physically moved close to them. It was like the 3 Ap’s had created a triangle of wifi signal and when I powered off one of them it was like there was a dead spot. From further testing with windows 10, macbooks, and android phone they all had the same reaction. I could tell from wifi signal testing that I had strong, 57, signal from SSID’s via the other 2 Ap’s but they would not connect unless I walked close to the Ap or to the Ap’s area that the powered down AP never serves.
Is there a maintenance mode I should put an AP in to? Are these Ap’s auto sensing eachother and tuning their power accordingly?