Are these slow growers? Mine puts out a new pseudobulb about once a year. It has no bugs, no bacteria/fugus problems -it's just slow. Regular watering with somewhat drying out between, 2500-3000 fc of filtered direct sun for 3-4 hrs, then about 750-1500 fc indirect light. Medium-small bark with coconut husk, charcoal, those fake white rocks, and little bit of sphagnum. Fertilizer is 10-10-10 about every three weeks.
While all orchids are reasonably "slow growers" in the plant world, plants in the Oncidiinae family are typically pretty active.
My first guess is that you're not giving it enough water, as they tend to prefer nice, even moisture to go along with the airiness around the roots.
Second might be the amount of feeding. Personally, I don't recommend feeding less-frequently than every two weeks, but using a 10-10-10 every three weeks, I'd mix it at about 2 teaspoons/gallon.
It should be in a constant cycle of flowering and growing. What are your temperatures? Is it getting calcium and magnesium? I would up the fertilizer considerably, too. If I used 10-10-10 I would fertilize every 2-3 waterings.
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My experience is that with most Oncidium-alliance orchids for the first few years they will only produce one lead and hence one new pseudobulb. Usually only one per year. That might happen for, say, 3 years. At some point the plant will likely produce two leads - one each side from last year’s pseudobulb. The next year if conditions are right both of these leads will produce two each - so its effectively growing exponentially from there on in. I just looked at my Charles M. and it appears it produced 13 pseudobulbs last year - but I don’t doubt it went through that same phase of producing just one new lead for the first couple of years I had it.
So slow at first, then rampant.
Yours looks very healthy. My main concern would be light - bright filtered light for just 3 hours isn’t much - mine get that all day long.