Can't see much of the plant, but what I can see seems quite healthy. The lifetime of flowers and buds on a newly-acquired plant doesn't say much about the health of the plant - flowers and buds in general tend to be very sensitive to changes in environment, that are inevitable when a plant goes from wholesaler to store, or gets shipped from the vendor.

The leaves look a bit dark for a Miltoniopsis... those tend to be rather light green. So it may not have been receiving sufficient light, either when it came to you, or under your care. But can't tell much from the photo, it may just be the lighting.

My bad.
Pls see these new ones.
Are the yellowing foliage all "old"? Are they not sick?

Those just look like old leaves to me. Force of nature. Older leaves, and even the small bottom leaves of newer ones just do that.

Now that I know what is a Miltoniosis for sure ..hahaha my doubtful due to always confusing Miltonia o Miltoniosis, however for me in the culture there are not much different.

They have up's and down with no reason. But when I see them down (yellow leaves on the bottom or onion types of layers), 1) cut the spikes. 2) Move them from one pot to other with out actually touching the roots, is more like a refresh and move the bottom than messing around the roots. 3) Cutoff running too much water (no bath or leaving water under a plate or pot holder); watering fast any time is need it and a little fertilizer every 15 days, so I keep the roots always humid (no damp) and 5) give it more light than to a phal, bright shaded light that don't transmit heat. They are very sensitive to the heat.

Sadly, I did find a psudobulb out of 2 turning brown inside out. That's why flowers are dropping. It is a bye bye...

I have had success getting a Miltoniopsis to regrow from just one bulb after the rest had rotted off. May take a while but worth the effort if you really like the plant.

Sadly, another miltonia having buds gone before fully opened... This one also looks fine otherwise though, unlike the previous one.

the reason these might be a bit harder is also the condition they get sold in.
The media is cheap rubbish that needs to be replaced, the roots are usually already damaged, a bulb rotting doesn't surprise me. I would remove both of them and give them a really good rinse under the shower. Imagine you are washing some hair that has brown gunk stuck to them that needs to be washed off. I really get into the cracks and crevices. Obviously you try not to damage any roots but the degrading material around the bulbs needs to be removed as a main priority with these. Otherwise you can't get it wet and as soon as you do you think oh no I have overwatered my orchid.
But they need water, it's all the rotting stuff left stuck to the bottom of the bulbs that is the problem, once it gets wet it starts to rot which then spreads on to the bulbs

Thanks. I will do that soon. I hope they are at least resilient upon a good cleaning. Neither of them has new growth though. I hope it isn't a big problem.

---------- Post added at 05:17 PM ---------- Previous post was at 05:13 PM ----------

I tried 2, 3, and 5 already and still see no improvement. I even transferred them to slotted pots for improved drainage.
May I ask why you cut off spike when seeing bottom leaf turned yellow? Aren't they supposed to being the oldest foliage?