Regarding weather; sometimes I also get bad weather/snow, even if I made it sunny the first time in editor. I have stopped speculating why. I just close TS, restart it, then again go into the editor, set my own weather again as first thing to do, then save.
For another reason I won't speculate about, my cloned "Hardship Harbour" (H_L) let me set weather my first edits, but no more. I get zwangs 22:30 no matter what daytime I set. But my chosen weather is fine. I'll get back to the issue if I find an answer. Maybe never :-p
It seems to me it has nothing to do with swapping locos, as this happened when I just cloned the H-L mission and set a sunny daytime, did nothing more.
Latest (a tad off topic): At Hamburg Wandsbek I have a Railpool vR loco on siding two, in my opposite direction. Time set so he will try to leave as I arrive. I get a red light and can go no further. You know why? Because the Railpool consist go bakwards off siding two, then drive into siding 1 and stops there. Which is my siding!!
At that point I leave my mission. I can only conclude the editor and/or H-L signalling is totally whacked and full of ghosts.