Hi Riz,
according to the phase model GET_DEFINITION is completed for all UIBBs before GET_DATA is being called. But maybe you run e.g. in OVP having collapsed UIBBs and lazy loading enabled in FLUID, so this should be disabled.
One option is to raise another FPM Event in IF_FPM_GUIBB_LIST~GET_DATA such that the Chart UIBB can react and apply on these.
Another option is to go for wiring, but this requires a bit more time and implementation effort.
Regards,
Simon