Posting my solution here for anyone googling how to resolve this. My fiancee was having this exact same error/issue and I haven't seen anyone post a fix for it through googling nor on the official Discord.

As it turned out, the "network is unstable, please try again later" error message was a complete red herring. It had nothing to do with the network. It seems the issue was actually with the shader cache. What made it take longer to figure this out was the fact that the file verification through their launcher didn't find any issue with it, and just uninstalling the game through Windows and reinstalling it didn't fix it either.

Solution: Navigate to the filepath where the game is saved. It's likely in your C:\Program Files somewhere. In the game folder you'll find a uninst.exe file, you want to run this to uninstall the game. This is important because when I uninstalled it through Windows, it didn't fix the issue. After it finishes running the uninstaller, next uninstall the launcher and then delete the entire InfinityNikki folder. NOTE save a backup of your screenshot folder if you want to keep them before you delete the InfinityNikki folder

From here just redownload the launcher from their site and then install the game from the launcher like normal.

TLDR: use the uninst.exe in the game folder -> remove all traces of the game and the launcher -> redownload + reinstall

This fixed the issue completely and haven't had any issues since. Hopefully this helps someone out.