Weird Lag Issue (Experts)

Hello epvp , We are running a Server and got a weird Lag issue. In general the Server aint laggin (just sometimes for a second) but whenever a character buys something from any npc or upgrade skills, its like lagging non stop, just for the one upgrading the skills.
While that, no errors shown on the Server side, SMC shows 0ms, rest seems fine too.
So if any of you got a suggestion, i would appreciate it

Probably because of logs, you can disable every log that is not that important

i already did that long time ago , but lag still there , :x