As pointed out the resize process is working at the rbd level but targetcli is not picking this up.

The process to resolve needs the dm device to be resized for targetcli visibility - currently looking in to the best way to do this.

For the Linux client - it's straight forward;
iscsiadm -m node -R .... to rescan connections
mulitpath -ll to list the devices
pick the dm name of the device that has been resized
multipathd -k'resize map /dev/dm-X' ... to pick up the changes

Patch applied on my local repo - currently testing - should release tomorrow.

please retest with 1.3 version. multipath devices are now refreshed across gateways when an rbd is resized, allow the new size to be seen by targetcli and the client OS

Verified in version:
ceph-iscsi-ansible-1.3-1.el7scon.noarch.rpm

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2016:2817