I tried a pair of Yongnuo YN‑600EX‑RT's with YN-E3-RT E3-RT E3RT TTL Wireless Transmitter in Multi/Stroboscope mode today and the 600EX‑RT's would only fire a single flash. I've done it a few times with one 600EX‑RT on the camera and it worked. Will Multi/Stroboscope mode not work in wireless mode?

