I experience something very similar running on Linux, glad to know this is also a Windows issue.
In my experience this is a totally random situation - most of the times it happens when driving at random points, but sometimes it happens even when you just load the scenario. I lowered graphics settings - LOD bias, disabled mipmap streaming and set textures to 1/2 res, lowered render distance to 1250m, tweaked some other settings but still it eventually falls apart. When it happens Linux closes the game because it hogs my entire 32GB RAM. Logs in game have very interesting bits, especially "[2026-09-04 17:44:07]: Unloading 1347 unused Assets to reduce memory usage. Loaded Objects now: 1036014." - 1 million objects? And then followed by a bunch of messages or errors from game scripts.
I do think this is related to the game randomly loading way too many copies of the same object. When going from Warszawa Wschodnia to Warszawa Centralna in Łódź-Warszawa DLC I had two cases where I somehow managed to control the game and get some extra symptoms. First time I managed to enter pause menu in 2 FPS just as it happened, navigated to graphics settings and lowered render distance by 200 meters. The game started running smooth again, but after driving for 200 meters the framerate dropped again - presumably the 1 million of objects that were loaded had to be processed and rendered by the game again. Second time I reached Warszawa Centralna and the framerate dropped again, however this time I happened to workaround it by pointing the camera at the floor - must've been a part of the scenery in the Warszawa Centralna station that got loaded in 1 million copies again and frustum culling optimized it out, which let me drive past it. Once I left the station and the tunnels it was fine.
I do want to point out that this does not necessarily happen just in Warszawa. First time it happened to me when arriving in Skierniewice from Łódź on an IC Łódź-Warszawa route. Just today (log attached - SimRail_log_2026-09-04_16-11-07.txt) I tried doing the regional Skierniewice-Warszawa route in Impuls 2 and just as it loaded it lagged and eventually the kernel stopped it. Similar with the other log - SimRail_log_2026-09-04_17-40-43.txt - where just as I started to set up ED250 on Kraków-Warszawa EIP scenario, the framerate tanked and eventually the game got stopped by the system again.
