I purchased a Hisense 55H8F TV from Best Buy back in 08/2019 (08/02/2019 to be exact). Recently, I've been having problems with the TV - the wi-fi on/off setting (in the Settings menu --> Network --> Wi-Fi) keeps turning the wi-fi capability of the TV off while the TV is in standby/off. I don't know if this is a result of a firmware update that may have occurred or if it's a hardware failure that may not be repairable.
To explain further, last night I was using the TV. It was connected to my home wi-fi network, everything was working well. Using the remote control, I powered off the TV. I left the room to go eat dinner - no one was in the room for this time period. After dinner, I went back and turned the TV on again. As soon as the screen came on, the TV displayed a notification across the top that "the wi-fi setting is turned off" (or something to that effect). This has happened 5 times so far this week, so it's not just a fluke. When I get this notification, the only way to get wi-fi back is to go into the TV Settings --> Network --> Wi-Fi and manually toggle the wireless functionality back to the on position. Consistently when I do this the TV will immediately find and connect to my home wi-fi. I have tried everything from switching the TV's wi-fi connection back and forth between the 2.4GHz and 5GHz bands, factory resetting, checked for all firmware/app updates, all to no avail.
What firmware are you on? I was having a few issues, not exactly the ones you were having but I contacted hisense and they gave me a firmware to update my tv that wasn't available by using "check for updates" in the os. It solved my issues and it included some new things such as youtube hdr and prime video.