It seems I found what is causing the issue:
<189>Sep 15 2021 21:11:10 SW3-P-01 %SHELL/5/CMDRECORD(s)[581282]:Recorded command information. (Task=EZOP, Ip=**, VpnName=, User=_system_, AuthenticationMethod="Null", Command="dhcp enable")
<189>Sep 15 2021 21:11:10 SW3-P-01 %SHELL/5/CMDRECORD(s)[581281]:Recorded command information. (Task=EZOP, Ip=**, VpnName=, User=_system_, AuthenticationMethod="Null", Command="undo dhcp enable")
some process of system (User=_system_) is changing the config (DHCP config) several times per day, like a scheduled task
this forces the VRP to send a copy of config every time this task runs
now the difficult part: how to disable this task...