I've browsed reviews of flasher relays on Amazon, and apparently other people have had the same problem when going LED on all 4 flashers.

Some have said that this one that has a ground cable and it fixed the problem:

https://www.amazon.com/CEC-Industries-EF32RL-Flasher/dp/B00JXLH7CG/ref=sxbs_sxwds-stvp?keywords=motorcycle+led+flasher+relay&pd_rd_i=B00JXLH7CG&pd_rd_r=375d922a-74d3-4acc-ba4d-caea35c27460&pd_rd_w=IWfmy&pd_rd_wg=8TbUc&pf_rd_p=a6d018ad-f20b-46c9-8920-433972c7d9b7&pf_rd_r=5AZFHPYHPEF7RGPBQCXY&qid=1565910556&s=gateway