We got the same problem... we already started the third park and after some time the save gets corrupted or anything else, its really frustrating..
We play on the latest dev build without the launcher only in Multiplayer with 2 people. The Map we use is "Build your own Six Flags Park".
We both use Win 10 64 bit and the german version of RCT2 : Tripple Thrill edition from steam.
Would be nice if you could look over our savegame too.
DreamlandV3.sv6