I'm fairly sure you posted this elsewhere, given the 2017-thing seems rather specific, so ...
You're making the mistake of conflating all problems with lag as the same problem ... Of course, since the game is built on java, we've always been fighting against the garbage collector and it's uncontrollable pauses, off and on, since the game's inception. We fix it and inevitably an update months or years later adds new trash that then needs to be sorted itself. In that sense, certainly we've been dealing with this for a very long time now.
But, in general, the lag I'm aware of In build 41 is mainly on AMD cards running on Windows, driving around for a long time without seeing zombies causes the game to lag until either a zombie is spotted or the client is restarted. Another common cause (graphics-card/OS agonistic) is just slow mechanical hard drives unable to deliver chunks fast enough; if chunks bottle neck, you get a pause until it can be loaded.
These is different from lag that just happens because you zoom out too far, or there are two many zombies on the screen, or because it's a system with integrated graphics and is running out of RAM (or it's just ultra low power RAM), or it's a dual-core with hyper threading (thus the game thinks it has 4 cores when it only has two), or vysnc is enabled and the system can't keep up .etc. All can be described in similar manners, but all aren't the same problem. Going off an old thread that may or may not have had an answer or resolution doesn't mean we don't address issues.