Minecraft crashing when offline (router is disconnected)

So my router has to be off sometimes because i’m resetting the wifi but whenever i start playing minecraft, the game won’t let me play more than a few minutes before freezing and crashing. sometimes not even one whole minute. and the freezing lasts for a few minutes before the game actually crashes. minecraft also just opens up to a white screen when i get on it. the game will not let me save and quit too, otherwise it will just freeze again. note: this is all happening offline. the freezing and crashing happens every time without a doubt and it won’t stop unless i turn the wifi back on.thats when everything turns back to normal for some reason.