Your (near-)infrared remote is probably having trouble competing with the infrared energy coming off the fire. The camera's remote receiver is seeing the heat coming from the fire as so much brighter than the small amount of energy emitted by your remote that the remote's signal is getting lost in the noise.

If you want usable consistency in the environment described in the question you're probably going to have to give up the idea of an infrared remote and either go with a corded release cable or a wireless solution that uses a combination of radio (not optical infrared) and a receiver with a wired connection to your camera's cable release port.

Corded cables are the cheapest option for most cameras. I use generic corded releases and for the most part if you avoid the very cheapest ones they are fairly durable. Regardless of the shape of the connector, for the vast majority of cameras they are just basically unpowered switches. Even wired release cables that include a battery powered built-in timer (intervalometer) can usually still be used without batteries by manually pressing the release button on the remote.

Radio remotes are an extension of the wired release cables that place a radio transmitter and a radio receiver between the release button and the wired cable port on your camera. The receiver connects to the camera in the same way as a wired remote would. The receivers often can be mounted on the camera's hot shoe, but the communication with the camera is still via the wired remote port on the camera. They tend to cost more than the wired cables, but generic version are still fairly affordable.

For the Sony connector on your α6300 there are plenty of affordable choices available from third party suppliers. They come in basic form as well as with built in intervalometers. You can also get a radio remote with or without an intervalometer. You can even get one that allows you to control some Sony video cameras' zoom for video as well as the shutter release for stills via wireless radio.

The radio unit with built in intervalometer can also be used with a wide variety of other cameras via optional connector cables for such connectors as Canon N3, Canon E3, Nikon 10-pin, Olympus, etc.