Random-mixture GICs such as stage-2 NicMn1-cCl2 GICs and stage-2 CocMn1-cCl2 GICs provide model systems for studying 2D random spin systems with spin frustration effects. The magnetic properties of these compounds have been studied by de and ac magnetic susceptibility, and low field SQUID magnetization measurements. An irreversible effect of magnetization for stage-2 NicMn1-cCl2 GICs (0.8 less than or equal to c less than or equal to 1) and stage-2 CocNi1-cCl2 GICs (0 less than or equal to c less than or equal to 1) indicates an occurrence of cluster glass phase below a critical temperature where the spin directions of ferromagnetic clusters are frozen because of frustrated inter-island interactions.