Aerangis articuluta leaf yellowing

[floempie01]

Hi!
New user here! not a lot of experience with orchids, starting buying some during corona, to give me something to look after and care for.
Recently my aerangis citrata quickly lost its leaves, and although the roots still look greenish, the stem looks blackened/woodified. Don't know if that is the correct term but it looks like it has turned to wood.

Now my aerangis articulata suddenly has a yellow leaf that also turned completely yellow in about a day. Can this be related? I was thinking virus infection perhaps. I keep my orchids together in a small glass closet, but the other non-aerangis orchids have not been affected, so far.