Could be that there are to many devices, @miway80 had a simular issue with too many devices, but has never been truly confirmd, see the discussion here: https://github.com/rytilahti/python-miio/issues/650#issuecomment-643493440
You could try removing the devices and see if it then works, but I can imagine you do not want to go through the process of removing all those devices and then having to re-add all of them…