Why would my speed increase so dramatically after rebooting? I rebooted last night as well with similar results. I have an iPhone 8 running iOS 12.4. Does this seem more like a router or a phone issue?
It’s a computer issue in general. Fewer programs running, but also the computer uses the reboot process to clean up bits of debris from memory. In virtual space as in meatspace, a better organized space is one where work is done more quickly; all computer processes are speeded up but that one is one you can perceive and measure relatively easily (more easily than for example “how long does a program take to open”).
ISTM that if it were one of your hypotheticals, then the problem wouldn’t be consistent and reproducible. Mine is.
I spend most of my day connected to a different wireless network at work. I’m going to try a DHCP reservation on my home network (where the problem is) and see if that helps. In the past, I’ve also been able to resolve the issue by “Forgetting this network” and reconnecting. That leads me to believe that it’s not necessarily a resource issue as mentioned above.
Do other devices on your network behave similarly when they are rebooted? Some ISPs use a “leaky bucket” model of bandwidth allocation, where you get a high bandwidth briefly immediately after you connect, then when you’ve “filled the bucket” you start getting a lower bandwidth. Depending on exactly how the ISP determines that you’ve “just connected”, that could happen after a reboot or even after a wifi disconnect/reconnect.
Most people totally misunderstand how iOS works with background apps. Unless it’s actively doing something like playing audio (music, podcasts, etc.) or GPS tracking, then all those apps you see in the app switcher are literally just screenshots. They’re not running at all, or they’re in a frozen state. Apps that use background refresh services, such as to check for messages, email, new downloads, etc. would also resume that activity after a reboot, so it could actually make the phone slower until things settle down.
So the connectivity to the nearest access point would be my first thought. iPhones tend to “hang on” as long as possible to whatever access point they’ve connected to, even if there’s a much better one on the same network. Rather than forgetting and reconnecting, simply try turning off wifi or switching airplane mode on and off.
My guess is that it has to do with the speed of the wifi connection. As wifi signals get weaker, the connection speed drops. It often will not come back up. Rebooting, or going to airplane mode and back, or anything which forces the connection to be restarted, will cause the wifi connection to start back at a higher speed.
This can be particularly striking when going from 5Ghz to 2.4Ghz. Some wifi access points will do band steering, in which they will try and connect you at 5Ghz, which is much faster, and then if there are problems will bring you down to 2.4Ghz. I’ve never seen any that will go back to 5 without a disconnect/reconnect cycle.
Is there an app for IOS that can show details of your actual wifi connection? It should say something like connected at 2.4Ghz, channel 11, -61dbms, 144Mbs. Then you can look at that, and see if the connection has dropped to 56Mbs, or even lower.