explanation(s), please

[Annie Grieshop]

A small Brambach grand did something yesterday that has left me bamboozled.
I'd appreciate any information, suggestions, advice....

When I got there, the piano was surprisingly well in tune, considering its
overall condition.  Two trichords in the 6th octave (below the break) were
playing chords, but the rest was pretty OK.

I pulled one of the offending notes into tune, and almost immediately one
string went "BANG" and dropped pitch, taking the other with it.  I pulled it
back up -- no, it had not broken -- and then both of them did the same thing
(big BANG, very flat).  I've had that happen after treating pins with CA
glue, but never before, and I hadn't treated any of them at that point.  (I
did later, but it didn't have much effect.)

Here's the part that really confuses me:  after that happened, one string of
a 2nd octave bichord went terribly flat on its own AND a cluster of four
trichords just above the break in the 6th octave also spontaneously went
horribly awry.  I had not touched any of them.........

The plate does not appear to be cracked, and I didn't find anything else
that looked particularly suspicious.  What am I missing here (other than the
chance to call the trash collectors and get the thing hauled away)?  Thanks!

Annie Grieshop