Only can reachable one day

It looks like the instance ends up being unresponsive after gradual increase in load over the day. Depending on the instance type chose, you should check the CPU Utilisation / CPU Credits of the instance before you attempt a stop + reboot to rule out CPU bottleneck. Memory metrics are not available by default and you would need to configure CloudWatch agent for this. Another quick fix alternative, would be to switch to a higher instance type to check if the system uptime increases also. But that would obviously mean an increase in cost for that duration.

Based on the behaviour you described, I'd assume system resources being a constraint and the need to switch to higher instance type. But better to validate it with metrics

--Syd