For my home wifi, why sometimes, DHCP IP didn’t arranged by connected device and sometimes, some IP is skipped?

For my home wifi, why sometimes, DHCP IP didn’t arranged by connected device and sometimes, some IP is skipped?

For my home wifi router, I set Whitelist Mac filtering and set DHCP IP ranges from xx.xx.xx.33 to xx.xx.xx.40. I turn off router every night and turn on again in the morning.

When I turn on home wifi router, 1st connected device mostly get IP xx.xx.xx.33 and other connected device get ip arrange in order If I arrange IP by connected device order, They will be 33,34,35,36,...,...

But some times, They aren't arranged by connected device order or some IP is skipped Ex. If I arrange IP by connected device order some times they will be 34,35,36,33,...,... 33,35,36,34,...,... 34,33,36,35,...,... Sometimes 33 or 34 is skipped, no device get that IP

My questions is Does DHCP IP need to be arranged by connected device? Is it normal or serious if IP aren't be arranged by connected device or some IP is skipped.

I've checked router setting and connected device list and found nothing suspicious