Delay in reestablishing screen/ssh connections

[JCA]

    I am using a combination of several tools, so I am
not sure this is the right forum for my questions. My apologies if it
isn't.

    I have a Linux computer A that I have to put to
hibernate on a regular basis. From A, using both screen and autossh, I
open ssh connections to two remote Linux boxes, B and C. Both B and C
are in the same remote LAN; the only difference is that B has two NICs:
one for the external world (the one I use to access it), the other for
the LAN, whereas C has just one, for the LAN.

    The issue is the following: When I bring A back from
hibernation, shels that I had established with B become active again in
a matter of seconds, at most, whereas those established with C remain
frozen for some 10 minutes, before becoming responsive again. On the
other hand, immediately after reviving A I can open new ssh connections
to C without any problems. Indeed, I can attach straight away, without
any problems, to the screen sessions that were running when A was put
to hibernate. 

    Anybody have ideas about what might be going on, and
how to eliminate that 10 minutes waiting before connections to C get
reestablished?