i have bought several oncid and miltassia types over the last year that seem to go through this, and i think i know why... and you may be able to corroborate. is this a "plug" plant? is it loose in the potting mix, like not really established? there are numerous sellers trying to introduce plants in the 10$ to 15$ range that they buy from the growers as "plugs" meaning young blooming size plants that were grown in hydroponic plugs, like little chunks of florist clay, 2" squares. these were grown in ideal climates overseas and bought in mass by american sellers to pot up and sell to the public. the problem is that they are coming from a hydro or semi hydro environment, and then shipped long distance, sometimes bare root, and then potted up and sold over the internet cheaply in 3" and 4" pots of bark mix. some plants can survive this, and most take a long time to recover if they do at all. i am suspecting the best thing to do with these is to pull them out of the bark and grow in semi hydro. these are what i call rescue orchids for sure, because they almost always need intensive care. my success rate with these plugs so far has been about 35%. i now try to avoid these, but since they are so tempting with all the varieties i was wondering if i should try a semi hydro method next time. part of the problem is the middle man is not putting them into semi hydro, and sometimes they have it in bark too long before you buy it.