x64dbg terminates with "Debugging Stopped"

while debugging a file, suddenly, all registers get red and then debugger terminates with this message: "Debugging Stopped". this issue has happened at different location of the file and the debugger log just shows threads exit with status code 0.

• I increased the CPU, memory of my VM and it did not help.

• as it happens at different locations such as mv rbx, constant_value, I do not think it is related to anti debug techniques. and I could bypass it by slowly stepOver or put breakbpoint at a location after where debugger was terminated before.

• not sure if it because of debugging a new thread using same instance of debugger or not?