I've been testing the .NET core prototype on my pc and laptop and not noticed any bugs specific to .NET core. FPS is better 99% of the time by varying amounts and GPU usage is quite a bit higher, partly due to higher FPS, but even whilst being on the main screen with max fps limit hit which is strange. CPU usage slightly lower than .NET framework.
Interestingly, on my pc Cosmoteer runs almost entirely single-threaded, it pushes one thread to 80% while only using the the other 11 at 25% or less. On my laptop however the game balances perfectly between my 2c/4t CPU, pushing all threads to about 60%, whilst the game is getting about 2 FPS and GPU usage is at <5% 🙁 (My ram usage is at 80-85% usage though so that could be bottlenecking Cosmoteer.)
Initial load times (when Cosmoteer says running game for first time, this may take longer than usual) are noticeably longer on .NET core, however normal load times have improved by about 32% by my testing and maybe it's just me, but other things in-game which take a while to load, like creating a game, seem a bit faster too.
(PC: Windows 10 64 bit, AMD 1600x, 16 GB RAM, Nvidia GTX 980)
(Laptop: Windows 10 64 bit, Intel Pentium 4415y, 4 GB RAM, UHD 615)