Why does the dhcp server on Mikrotik change the ip addresses of clients on the network?

Question

DHCP

Hello!
Set up dhcp server on Mikrotik. All settings left by default. The only thing that has changed is Lease Time=15d.
The problem is that the ip-addresses of the clients on the local network change. On the server itself, the old addresses "hang" with zero MAC addresses and with the busy status. They do not display active MAC addresses or hostnames.

Answer 1

the problem is what? there is a free pool of addresses. there is a pool of addresses occupied. as soon as the address is snapped off from the busy ones ... it queues up for distribution according to the priority of the logic of this very distribution. not satisfied? assign static! if the poppy miraculously changed at the network card when the computer was restarted (it happens) .... the address will receive a new one.
I also don't see the point in such a long lease of addresses. maximum rental per working day is given.

Answer 2

Add a couple of addresses to dhcp server --> leases --> Make static
See if users continue to use them?