pfSense

dhclient will attempt to use a previously successful recorded lease if it cannot contact a dhcp server.
However it will use the first recorded lease even if that is conflicting with another interface. In the even that IP is already in use on the firewall that can break connectivity.

For example here the IP address 192.168.206.2 is already in use on another VLAN that shared the same parent interface (and hence MAC):

Jun 14 16:37:06    dhclient    37058    DHCPDISCOVER on mvneta0.4092 to 255.255.255.255 port 67 interval 8
Jun 14 16:37:15    dhclient    37058    No DHCPOFFERS received.
Jun 14 16:37:15    dhclient    37058    Trying recorded lease 192.168.206.2
Jun 14 16:37:15    dhclient    22858    TIMEOUT
Jun 14 16:37:15    dhclient    22973    Starting add_new_address()
Jun 14 16:37:15    dhclient    23104    ifconfig mvneta0.4092 inet 192.168.206.2 netmask 255.255.255.0 broadcast 192.168.206.255
Jun 14 16:37:15    dhclient    23642    New IP Address (mvneta0.4092): 192.168.206.2
Jun 14 16:37:15    dhclient    23955    New Subnet Mask (mvneta0.4092): 255.255.255.0
Jun 14 16:37:15    dhclient    24128    New Broadcast Address (mvneta0.4092): 192.168.206.255
Jun 14 16:37:15    dhclient    24314    New Routers (mvneta0.4092): 192.168.206.254
Jun 14 16:37:16    dhclient    37677    New Routers (mvneta0.4092): 192.168.206.254
Jun 14 16:37:16    dhclient    37965    Adding new routes to interface: mvneta0.4092

Tested in 22.01 on an SG-1100