Thanks for the contributions, matanza & @drbob. I'm keen to know if the Fibaro bypass works better too.
For me and my setup, however, everything is still working 100%, ever since enabling "Dettached Switch" mode and updating the firmware. Wish I had held off on updating the firmware to see what fixed it but if I were a betting man, I'd guess that changing to dettached mode is what sorted it out.