Zygo breeds dropping leaves

[Syrinth]

Hi, I have a few zygo breeds, snowbirds, advance australia and mathina elizabeth.

I really love these flowers and how they look, but this past year, all of my zygo breeds have defoliated. By this I mean, all leaves gone, they all turned yellow in the middle with a single streak which spread out until the leaf dropped off.

Now I have several plants with pseudobulbs but no other leaves. Two of them have since put forth a new shoot and the leaves are... okish but one of them, the snowbirds I think, has the leaves starting to mottle again.

The mathina elizabeth wound up having no roots and it's currently in a high humidity chamberand I'm praying for the best. It had a new growth but it didn't make it.

any thoughts on what could have cause this? My room isn't the most humid, it seems to float around 50 during the winter, and it gets surprisingly warm (90 F during the day)so that could be a factor...