I think the higher end Fortigate appliances seem to get shipped with a pair of FN-TRAN-SX SFPs as some sort of "gift" to allow you to connect to switch uplinks or something. They don't get obviously listed in the order or spec sheet (I think).
I've now been twice burned by having remote engineers doing installations on my behalf thinking they are being expedient and are installing the FN-TRAN-SX (1000BaseSX) SFP transceivers into my projects instead of the ones we ordered separately (usually 10G-SR or 10G-LR). The first time it happened was when engineers arriving at the data centre "debox" all of the equipment in the loading dock or staging room (often a requirement to avoid combustibles staying around). Because we had two types of switches and gave instructions to make sure they match brands (the switches report compatibility issues otherwise) that seemed to be the "heard" instruction and the wrong SFPs ended up in the Fortigate.
On this second job (unfortunately I was on vacation) the same thing happen, but this time the site engineer hadn't located or seen the box containing the other 10G-SR SFPs and so "presumed" the SX ones were the correct ones. Unfortunately because SR and SX both use the same 850nm wavelength, you get spurious "link up" indications on both the switch (which had the SR) and the Fortigate with the SX. But because it was all intermittent and flappy (LLDP would work some times, LACP would half work and we configured things as a Active-Active cluster - something new to me) we hadn't actually focussed on the real PHY layer issue. We literally lost days chasing this down.
Anyway, I guess my take is that 1000BaseSX is pretty much last century stuff now, so I am really wondering whether anyone has similar war stories and maybe if Fortinet still want to ship them they should put a label on them something like "THESE ARE NOT THE SFPs YOU ARE PROBABLY LOOKING FOR!" ;) FortiGate #PHY #SFP #Tranceiver