Many of them are embedded sensors and some other embedded devices.
I have a dhcp "static IP" reservation using the internetbox plus for each one of them and a monitoring tool to track that all of them remain connected.
However the internetbox plus removes the fixed reservations from time to time. I can confirm with the monitoring tool that all the devices have been connected properly all the time.
There is something in the dhcp server of the internet box that is cleaning things too much (reservations start dissapearing after a week...) I would prefert that static IP reservations were not cleared at all. After all, this is an expert feature, and the removal of the reservaion based on the MAC address should be manual too.
This behaviour is quite unpleasant, because those devices connect via mqtt or other protocols to exchange information, so when the ip adress change arbirarly everthing gets screwd up.