rockm

Japanese andromeda are senstive to 'wet feet' as bonsai. They don't like soggy soil and react in a manner like you describe when they develop root problems. Overwintering on a fire escape or balcony doesn't provide protection from fluctuating temperatures and too much moisture. It's a difficult thing to protect against.

I'd take a look at the roots of the plant to see if they're rotting. If they are, an emergency repot into more freee draining soil may be necessary.