Just in case if someone have\had the same problem.
I finally managed to fix it. I gave up a long time ago, but then i returned to this problem and spent like two full days, trying all possible and sometimes really stupid solutions. Including Disney and GoG techsupport.

Long story short: it happens when you connect to the server with 20\30 TPS without /framelock option, so game runs on 60FPS, server runs on 30 (or 20) TPS, game tries (i assume) extrapolate this (like, 30TPS logic to 60 FPS output) and we have such problems like mouse deceleration, glitches with grenades etc. So, game won't allow you to set TPS tru interface, so you have to use comman line or SWBFspy software (as i did). Because, well, game lets you create server only with TPS=20 with no options to change that.

Solution is simple yet tricky: you have to start the game with /framelock parameter, so you will be forced to play with FPS=TPS of server. Another workaround (if you don't wanna play with 30 FPS) is to create server with 60TPS while use /framelock,

Hope this helps.

Many thanks, i'll try this one.

Not wireless, only wired mode.

UPD: Well, that didnt help.
Tried on three PCs, on Win7 and WinXP, with different mouses. Same aiming issues.
Its easy to notice the difference between mousepointer in main menu and in online mode.

Quote from: Led on June 19, 2018, 09:35:03 AM
Are you using the GoG servers or our SWBFspy servers?

I don't know, to be honest. I use Steam vanilla version of game, so i guess, Steam servers is in use?

The thing is - in any kind of singleplayer mode (campany, instant), things totally ok: everything smooth and precise.
But even if i create LAN game as host (i have a real LAN connection here, without third-party software), and play alone, as host, things get worse. Mouse pointer is laggy, aiming (in both 1st person and 3rd person modes) is accelerated, grenades looks laggy, lightsabers looks laggy etc. Besides this, everything is totally ok.

I know that bad connection can create some lags and things like this, but i can't understand, why such things happens when i create a LAN game in my LAN. It looks like those things just hardcoded for online mode, but why?

(sorry for my english, but i really need help with this, and russian community is dead)

So, basically SWB2 plays totally okay when in singleplayer mode.
But im only get laggy mouse movement (not only aiming, but pointer in menu, too), even when i am host
And it happens only and only when i create or join online (internet or lan) game.

https://steamcommunity.com/app/6060/discussions/0/1488866813770626421/ - this dude totally described exactly the same problem. Anyone know how to fix it?