Pppoe server internal pool ip addigning issue

I am facing massive user disconnect issue. I checked with radius team. They told its pool issue users are not getting ip addresses. And also I noticed that internal pool ip addresses are not assigned in order. Some ip adresses are skipped between one user to next user. Like user 1 got ip address of .1 and next got .7. why gap

as u can see I have shared screenshot

4,6,18,23 these are missing in this screenshot only

“reset pppoe-server interface all”
command does nothing. Once router is rebooted issue is resolved. I this ip addresses are not freed and reused once user is disconnected.