Flash for G9

Have you checked that the lock levers on your FL580s are actually pushing the locking pin out?  That would be the most likely culprit for a loose connection: that or not seated the speedlight far enough forward into the hotshoe for the locking pin to engage in the locking hole on the hotshoe.

Agreed, though: firing at full power indicates the TTL pins aren't making contact.

CaineBCN wrote:

I use the Neewer TT560 without any problems.

aka the Godox TT560, as far as I can tell.   But manual-only flashes can be a pain if you're event-shooting.

I'm a Godox TT350-O (on-camera) or off-camera TT685-C (w/XPro-O) shooter.

Godox makes six speedlights. There are three models, with two versions each: the AA powered (TT) version or the rechargeable li-on battery packed (V) version.  The V versions do not have external battery pack ports, given that the packs have roughly 2.5x the capacity of a set of AAs (they also slightly speed up full-power recycle by about 0.25s). The three models are:

• TT350-O ($85)  / V350-O ($160)  (new model; only the Sony version is released, but all the other ones are available for pre-order on Adorama).  Mini speedlight. 2xAA powered. So, lower power, only 270º swivel, no recycle beep, no sync port, no battery pack port. But perfect size/weight to balance on a mirrorless body. And can be TTL/HSS radio master.
• TT600 ($65) / V850 II ($140). single-pin manual-only flash. No firmware upgrade capability. But can be an HSS radio slave. Can only communicate flash power settings as a radio master (no TTL, no HSS), because of the single-pin foot.
• TT685 ($110) / V860II ($180). TTL/HSS radio master and slave. Also "smart" optical master/slave if it's the Canon, Nikon, or Sony version. 

All of them have a built in radio transceiver in the X system, which is why we like them so much. But for on-camera usage, there might be issues with AF-assist and TTL accuracy/consistency, as well as the stiffness of the head rotation adding torque on the camera hotshoe. Also, all the Godox speedlight still use a twist-lock, not a lock lever.

The biggest reasons to go with Godox are that they also make TTL/HSS bare bulb flashes (AD200, AD360II) and battery powered studio strobes (AD600, AD600M, AD600 Pro) in the same radio triggering system; and these lights are somewhat modular: the AD200 has an interchangeable head (fresnel, bare bulb, LED), and two can be mounted in a dual-bracket with LED modeling lights; the AD600 can, with accessories, be separated into a pack and head or used on AC power.

And the Godox radio triggers that are built into all the lights can autoswitch and perform TTL/HSS between the five supported systems: Canon, Nikon, Sony, Fuji, and MFT.