Thanks so much for your reply and advice I really appreciate it. I do give them high light and I also have strong LED lights so that might be what is happening. One of the plants pictured is a Dendrobium Farmeri so I am probably going overboard on the light.
Thanks so much for all of your advice, I really really appreciate it.
In the end I unpotted the plants with mold and cut off dead roots that were present and the repotted into fresh bark. I think that I didn’t get all the dead roots in the first repot and that this was the main cause of the problem to be honest. I think that I have managed to address the issue but I won’t speak too soon!