Main monitor suddenly becomes invisible when additional monitor added.

Grant -

2023 Mac Studio M2 Max running Sequoia 15.3.2

Samsung LC49J890 Ultrawide monitor - connected via Samsung supplied HDMI

small displays : Arzopa models Z1FC and A1 - connected via USB C directly to rear USB C inputs on Mac

As noted in original post all have been working perfectly together in this configuration for more than a year with no changes made by me to any refresh rates or other display settings. Only changes in this period have been regular Mac OS updates.

Update: have just determined that it is only the connection of the Z1FC Arzopa display that causes the Samsung monitor to be rendered "invisible' to the Mac. As the main difference between the Z1FC and the A1 Arzopa displays is that the former is marginally larger (17.1" vs 15.4") and it has a higher native refresh rate (144 vs 60). Changing the refresh rate on the Z1FC made no difference to the issue.

Thanks Grant. I have tried it with other HDMI cables with a similar outcome. What perplexes me is what might have changed that leads to this sudden change in behaviour after more than a year of normal operation with the current configuration. The fact that the new ‘disappearance’ of the Samsung only occurs when one specific smaller monitor is connected but not the other, only adds to the mystery, though the power angle you suggest might relate to that. It is the emergence of the issue without any apparent new change to the configuration that is the frustrating factor.