I have access to too many Androids and the one thing I learned is there is no always.
This model phone seems nice enough so maybe you can try a temp monitor app.
I bought a new phone (Galaxy J4+), it came this Monday.
Today at about 19:00 (Germany) I was watching YouTube. When I'd normally watch YouTube, the phone'd be very slow and not properly respond to my touch. The phone had that kind of behavior pretty often, atleast for the 2-3 days I've had it, but usually only when I was already using it for like half an hour. It would start very suddenly and slowly get faster again. When I stopped using it for a bit and came back later, it'd be normal again, so I thought it's just that the phone overheats and cools off when I leave it. This time however, when I was watching YouTube, it got slower and slower (I didn't realize until I had to think about what happened in order to resolve the issue I had later on). So I power off the display and leave to do some work for a few minutes. When I come back I power on the display and try to unlock it by swiping and entering my PIN. When I swipe, the numpad doesn't show up, the display is very slow and not reacting to anything I click on. I shut the display off and on again. Now not even the back arrow shows up when I swipe. The thirf time, the display doesn't even turn on, it just stays black. It heated up slightly when I plugged it in to charge, nothing else changed though. When I plugged it into my PC the PC registered the phone normally, with the phone model and everything. I tried to find a way to fix it online. Meanwhile someone from my family turned on our Xbox One. When they did, first they got no video signal, after restarting and making sure that all cables were plugged in correctly, it booted normally. The problem was, you couldn't log in. When you pressed on the button to log in and chose the account you wanted to log in to, nothing happened, even after restarting it several times. After shutting the Xbox down, unplugging the LAN cable and starting it again, everything went completely normal.-- Forgot to mention: When I tried to launch my PC the first time, the LEDs would light up, but I'd get no video signal. When I pressed the power button again, it shut down instantly, no time taken for it whatsoever. Second time trying to launch everything went fine. -- So I first disabled WLAN directly from my router and then, to be sure, unplugged it completely. When I did, my phone booted after I pressed the power button (no holding it down). The boot took way less time than it normally would, I got the normal animated Samsung logo when booting up too. What was weird though, is that I didn't have to enter my PIN to unlock my SIM card, which you always have to do after turning on an Android phone.
I don't get what happened exactly that caused that, it had something to do with our internet though, so much is sure. After turning the router back on, my phone worked normally (with enabled WLAN). If anyone could give me some insight on what might have caused everything, I'd be very grateful. I don't know if this is some kind of virus, our ISP fvcked up, there's something wrong with our router, or everything was just a coincidence (which I don't believe).