PSU drops both current and voltage when connecting to an LED
Specs for linked device say 30-34V, that should be your Vfwd. LEDs usually have higher initial Vfwd until they warm up, then it drops slightly. Could be that 30V is not enough to start it up properly. Once substrate has warmed up, internal resistance drops, Vfwd with it, assuming CC.
What PSU are you using? Could it be, that it has internal overcurrent protection and just flickers on and off? E.g. it turns on, sees too steep increase in current and just turns off as a self-protection measure?