Hiya Caroline,
Firstly, Akerne’s Rainmix is an excellent orchid fertiliser and I have used it myself for years. If you have applied it at the recommended concentration there should be no deficiency issues.
Such blotching can often be seen in the OLDER leaves of cattleya/laelias and is natural. If the newer leaves seem healthy I wouldn’t worry.
I have also seen similar blotching in orchids that have been getting prolonged strong sunshine and they recovered their uniform green appearance when transferred to the shade. If this is true in your case the problem should resolve over over the winter.
I don’t think it is virus disease as typically the symptoms would be yellow streaking/circular patterns/black pitting indentations (and sometimes flower colour-breaking).
So I would wait and see. Anyone else have comments on this?