This sound very interesting. If you remember some years ago I messaged you about a problem where splines were refreshing constantly and flickering, which turned out to be resolved by turning full v-sync on. Now I get a mix of what you are saying and my old problem. Basically, I imported a part of a route (a few baseboard). The initial route was huge (thousands of baseboards) and then i deleted all and kept just a station I liked (it was something swedish or something). In that are everything seems to be weird, exactly as you said, splines flickering, drops in fps (maybe not as bad as in your case). Now I really start to wonder if there could be a fix without erasing months of progress. My idea is that the merging process is what corrupts the area, not the initial route. Everything seems perfect on the initial route before the import.
I will tell you what other things I find exploring. What questions I would like to address are:
1. Does the merging process corrupts something in the files or makes something to be unsteady in the route?
2. Can a high number of splines (in the image below) cause flickering or problems?
3. Can this be related to hardware or gpu handling lods on the tracks>
I think it's a combination of things. V-sync settings have varied between video card drivers for the longest time and Trainz versions. At the moment, I'm using half V-sync because the full V-sync is too heavy, before that I was using none.
It's a weird problem, I know. This cutting in and out causes tracks to load S L O W L Y with big chunks missing. Roads and fences draw in up close and disappear very quickly only a few meters away. All the while this is occurring, buildings are really slow to load and the FPS drops to something like 5 FPS in that area and this only occurred in the session at first. Hitting pause while driving, would allow everything to load up again and the FPS was better. I had this issue once before due to some passenger cars with a faulty script. Removing these and replacing them with something simpler helped and that was the end of it for the longest time. Thinking this was corrupted rolling stock, I removed various freight cars in blocks based on content creators and replaced them with something else. This didn't help. The tracks and other splines still disappeared or started loading slowly in chunks and I had to hit pause. Once I did that, I could drive until I got to another big area. Since this started in the session, I thought it was some other scripted asset and I removed a bunch of interactive industries and this didn't help at all.
Having said that, I don't think it's the merging process that did this because everything was fine initially. One day, I loaded the route and noticed a building with spikes sticking out of it. This was one of those really old simple cube buildings that are very useful for making cities without causing routes to sink to 1 FPS. I took note of the building, deleted it from my content and downloaded it again from the DLS. A short time later, roughly in the same vicinity, I had another building that had problems. This one sent out shadows across the route and hunting it down was difficult because they would disappear when I got near the area. I eventually deleted that building from the route before downloading the asset again. Like the other building, this one will never be lost due to the sheer number of buildings in the area.
After I removed those two buildings, everything was fine and then in July, there was a big stutter when I entered the area from my own route which I blended really nicely too I may add. Once I rounded the bend in this built-up area, everything was fine. I removed a bunch of industrial buildings, some of which had really, really high polycounts and would never be missed anyway. This helped a lot and I was happy with the results. I also used the opportunity to clean up some things I didn't like in the area. The clean-up helped initially. Running the route a short time later after making changes caused tracks to disappear in various parts of the route again.
After some time, the issue got worse as if the route was rotting. I'd make changes such as removing a bunch of unneeded buildings because the area had buildings against buildings. This helped a bit, but then the problem came back later. I then started removing splines and lots of them such as grass splines. I was going to redo the route with TurfFX and PBR textures and the grass splines didn't look that good, and removing those was no loss. Again, this issue reappeared, causing death to the route. I also replaced many of the fences with others that always loaded fine or removed many of those. This helped a tiny bit.
With the tracks still drawing awful, I switched content creators and went to some built-in, or rather some pro-tracks from N3V from some DLC I don't remember. After replacing the track, everything loaded up and I was happy until the next day when the problem reappeared. I then did more culling after I found many old spline buildings from dmdrake in the city. They're really old and while they fill up areas, again there were way too many of them. I deleted a bunch that were in the background and put in some hills to create a break in the large vast sea of city buildings and industries. This helped a lot and I was happy again for another day.
Now, the problem is worse with, and the problem now occurs in the route editor and when editing in the Session editor when paused. Yesterday, I went back to a previous version of the route, long before the merger, and the problem isn't there. The splines load up fine, although I see some I'd like to replace now, but other than that, I don't lose the tracks in Surveyor. Testing in a driving session will be a whole other matter because I have to recreate the train consists again from scratch.
