This may not be your issue, as I do not have a HomePod mini as a hub for my Meross Smart Plug Mini's (MSS110):
My problem was that I had difficulty in connecting with the Meross smart plugs - eventually after some difficulty only getting connection to 2 of the set of 4 that I purchased in the kit.
However these then proceeded to keep dropping out (i.e. no connection to the Apple Home app) and then reappearing a short while later.
I also could not connect to the other 2 smart plugs at all!
After a few hours of struggling to follow the Meross instructions on getting a connection - I still could not connect.
So I eventually solved the issue by following the instructions on the Meross website to update the firmware in each Smart Plug Mini.
This was achieved by connecting my phone wifi to the local wifi of each Smart Plug and following the instructions on the Meross app.
However since you seem to have got connection to your smart plugs, I guess that all you would need to do is to use the Meross app to update the firmware on each smart plug.
Within the Meross app, select the 'User' symbol at bottom right of the screen and within that page you will see a 'Firmware Update'.
Select Smart Plug Mini and you will see if your firmware within each Smart Plug is up to date.
If not then it should enable you to update each plug's firmware.
I then found that they were rock solid and have since never failed to work 100%.
If this is not your issue then I apologise for taking your time!
I have the latest iPhone software and also an ipad with the latest Apple software update - both of these can now control all of my Meross mini smart plugs.
Best regards Keith
