iPhone 7 plus camera getting hot after logic board replacement

It sounds like there could likely be a bad connection between the camera and the logic board, fpc connectors shouldn’t ever be difficult to connect so if you had to “force them back in the connectors” its likely that its not connected properly. The fact that the camera is getting hot is more proof of this. Open up the phone again and remove the camera connector from the board. Take a good close look at the fpc connector on the board as well as on the camera and look for any bent/broken pins or any other debris that could be preventing the camera from making a solid connection. If pins are bent/missing from the camera you will need a replacement, if they’re missing from the logic board you’ll need to bring it in to a repair shop that does board-level repairs in order to replace that connector. When you reconnect the camera take care that the connectors line up properly and you’re not using too much force to connect them.