Not sure what type of call pickup you are referring to. In any case, you will have to start fop2 server in full debug mode and inspect the log when you attempt such a pickup. the pickup manager application does not work on remote servers (asterisk limitation), but I am not sure if you are using the pickup application or doing a simple call redirection.

Multi server setups require a well crafted dialplan, and if the dialplan is not the same in those servers, then some actions will fail (like sending calls to an extension@context that only exists on one server and not the other, etc).

To start fop2 in full debug

service fop2 stop
cd /usr/local/fop2
script capture.log
./fop2_server -X 511
(do your tests)
ctrl-c
exit
service fop2 start