The lmkd (low memory killer ) was somehow killing the forked init process and that was triggering lagging issue, making the forked init as unkillable solves the problem
1. Download and paste the magisklagfix.sh , in your internal sd card (not external sdcard).
2. Execute these commands:
su mkdir -p /data/adb/service.d && cp /sdcard/magisklagfix.sh /data/adb/service.d/ && chmod +x /data/adb/service.d/magisklagfix.sh
Old Method Temporary Fix: (Need to do after every reboot)
su for i in $(pgrep -x init); do echo -1000 > /proc/$i/oom_score_adj && echo -17 > /proc/$i/oom_adj; done
Refer here for more details:
Also thanks to @XPr1d3 for reporting this lagging issue to me and @kapmino269 for trying to help me out