Some photos:

Correct.

Thanks. I was hoping it was sun damage, but I was puzzled by the fact that it was the only plant with the sun damage and also the damage was in the middle of the leaf rather than the outer edges (which would be in line with my past experience). Anyway, thanks for confirmation. I was afraid it was fungal in nature.

I don't know what it is but it does not look like sun damage. If that is the only leaf affected, I would not worry about it.

There were 3 leaves, all on the same branch, which I removed. I guess I will have to keep an eye on the plants.