[Baertram]

Masteroshi, there is not any "1 addon" causing this!
It could be each addon, especially the ones that monitor all your buffs, abilities, combat and heal stats, sending data via groups map ping, inventory handling on item pickup, and so on etc.
Maybe some of them never heard of event filtering and check every single event any group member or palyer around you at the server fires...
Maybe they check all items in your invetory each time you pickup something, where this would not be needed.
Maybe your requipped items are checked eacht time you do any skill or change the weapon bars, just to find out if anything needs to be repaired / needs to be automatically changed because your active bar is another and you want a mythic item usage now, or different CPs applied, and so on.



I personally got lags and such with Fyrkains Minimap years ago and after switching to Votans Minimap it was resolved.
Same happened with some target / group frames etc. which I used with acustom UI addon starting with A (not sure about the name anymore).
Once disabled, all fine!

Also my CPU was a bottleneck once and after upgrading FPS were more stable (without addons)
Same with Nvidida drivers, enabling "Mode for low latency" to ULTRA, setting max FPS = 1 below my monitor's max refresh rate,
fixed screen micro stutters on my GSYNC monitor (without addons).


So disable your addons one after another and try yourself, which one it is.
It depends on your used addons AND their settings, so there cannot be 1 simple answer to your question, unfortunately.

Edit:
I often got stutterings (fps drop by ~50% al of sudden without reason) if I'm near the open sea e.g. at Sumerset and watch the sea if I stand near a Geysir, turning around to watch to the land even stutters more.